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Descriptive  Anatomy 


OF  THE 


Human  Teeth. 


FOURTH    EDITION.  i 


BY 


G.  V.  BLACK,  M.D.,  D.D.S.,  ScD. 


philadelphia,  pa.: 

The  S.  S.  White  Dental  Manufacturing  Co. 
igo2. 


IS?  7 


Copyright,  1S97,  bv 

The  S.  S.  White  Dental  Manufacturing  Co. 

philadelphia. 


PREFACE  TO  THE  FIRST  EDITION. 


BY  my  experience  as  a  practitioner,  as  a  teacher,  and  in  my 
intercourse  with  fellow-practitioners,  I  have  become 
convinced  of  a  serious  defect  in  the  teaching  of  the 
details  of  the  anatomy  of  the  teeth,  and  in  the  system- 
atization  of  the  terms  used  in  their  description.  This  defect 
has  been  a  constant  drawback  at  the  chair,  in  the  laboratory, 
and  most  of  all,  in'  the  college.  The  object  of  the  present 
volume  is  to  remedy,  in  a  measure,  this  defect.  To  this  end  I 
have  had  constantly  in  view  the  needs  of  the  dental  student  and 
practitioner. 

We  have  heretofore  had  excellent  general  descriptions  in 
human  and  comparative  dental  anatomy;  but  these  have  dealt 
principally  with  the  general  forms  of  the  dentitions  of  the 
mammalia  and  other  orders  of  animate  beings,  rather  than  with 
specific  descriptions  of  the  forms  of  the  various  surfaces  and 
surface  markings,  making  up  the  sum  of  the  forms  of  the 
individual  teeth  of  man.  Valuable  as  these  works  have  been, 
they. have  left  the  acquirement  of  a  knowledge  of  the  details  of 
the  specific  forms  of  the  humqn  teeth  mostly  to  individual 
observation.  By  this  means,  many  have  attained  to  an  excel- 
lent perception  of  the  various  forms  of  the  human  teeth ;  but  it 
is  not  reasonable  to  suppose  the  profession  generally  will  do 
this  without  some  fixed  guide.  What  the  dental  student  wants 
most  in  the  college,  and  in  the  office,  is  a  systematized  nomen- 
clature of  the  several  parts  of  the  teeth  in  detail ;  and  such  a 
description  as  will  call  his  attention  successively  to  every  part 
of  each  tooth,  as  Gray,  in  his  Anatomy,  has  called  attention  to 
every  part  of  each  bone,  however  apparently  unimportant.  It 
should  be  remembered  that  anatomy  is  not  to  be  learned  from 
books  alone,  but  also  by  bringing  the  parts  to  be  studied  into 
view,    and    closely    examining   them    in    connection    with    the 


IV  PREFACE. 

descriptions  given.  Anyone  who  may  read  the  present  vol- 
ume without  a  reasonable  number  of  human  teeth  of  each 
denomination  before  him  for  examination  and  comparison, 
will  be  but  partially  benefited. 

It  has  been  my  object  to  systematize  the  nomenclature 
most  in  vogue  with  the  profession,  whenever  practical,  rather 
than  to  introduce  new  terms.  However,  the  reader  will  find 
a  few  new  terms,  and  possibly  a  few  old  ones  that  are  used 
differently  from  the  former  custom.  The  terms  up  and  down, 
to  indicate  direction  or  parts  of  teeth,  are  abandoned,  because 
of  their  ambiguity.  In  a  few  instances,  new  forms  of  old 
words  have  been  used,  especially  to  avoid  the  terms  inner, 
outer,  backward,  forward,  etc.,  which  are  so  often  misleading. 
The  words  mesial,  distal,  labial,  buccal,  lingual,  etc.,  are  used 
as  adverbs  of  direction  by  adding  ly,  or  the  same  thing  is 
accomplished  by  the  use  of  the  preposition  to.  It  is  as  easy 
to  say  of  a  cavity  that  it  extends  far  beyond,  beyond,  to,  nearly 
to,  or  to  the  gingival  line,  as  to  say  it  extends  up  or  down,  etc., 
and  the  meaning  will  not  be  mistaken;  or  to  say  that  a  cavity 
extends  distally,  or  to  the  distal,  or  lingually,  or  to  the  lingual, 
instead  of  backward,  or  inward,  either  of  which  has  different 
meanings  in  different  situations.  The  best  rule  is  to  use  no 
extraneous  object  in  the  designation  of  the  parts  of,  or  direc- 
tion on,  the  surface  of  a  tooth ;  but  to  confine  the  phraseology 
to  the  specific  and  well-defined  terms  applied  to  its  several 
parts.  The  back  part  of  a  molar  would  not  mean  the  same 
relative  part  as  the  back  part  of  an  incisor.  In  many  such 
ways  the  author  has  endeavored  to  systematize,  and  make 
more  definite,  the  phraseology  applied  to  the  teeth  without 
going  to  extremes,  knowing  well  that  forms  of  language  once 
in  use  can  be  improved  more  easily  than  they  can  be  displaced 
by  new  terms,  though  more  exact. 

The  absence  of  a  Bibliography  may  be  noted.  The  plan 
and  object  of  this  work  has  not  seemed  to  call  for  many  refer- 
ences to  authorities.  This  does  not  imply,  however,  that 
authors   who  have  preceded   me,   as   Fox,   Carabelli,   Tomes, 


PREFACE.  V 

Wedl,  Judd,  Wortman,  and  many  others,  to  whom  we  are 
greatly  indebted,  have  been  either  overlooked  or  ignored. 

The  illustrations  have  all  been  made  by  the  author  for  the 
purpose  of  illustration,  rather  than  as  works  of  art.  After 
experimenting  with  the  various  plans  of  the  management  of 
light  and  shade,  diffused  light  has  been  used  because  more 
detail  could  be  shown,  especially  in  the  difficult  task  of  illus- 
trating the  occlusal  surfaces  of  the  teeth.  Each  picture  of  a 
tooth,  in  all  its  details,  is  drawn  from  accurate  measurements 
of  the  particular  tooth  in  hand. 

Much  of  dental  histology  might  properly  find  place  in 
this  book;  but  that  subject  is  well  represented  by  others.  Mal- 
forms  of  the  teeth,  supernumerary  teeth,  and  variations  of 
arrangement,  belong  to  the  subject  of  irregularities,  which  is 
amply  treated  by  several  authors.  My  aim  has  been  to  confine 
the  book  strictly  to  normal  macroscopic  anatomy.  However, 
a  very  serious  difficulty,  which  has  always  met  the  dental 
anatomist,  has  been  the  variations  of  form  in  teeth  of  the  same 
denomination.  The  endeavor  has  been  to  systematize  these 
under  one,  two  or  more  typical  forms  of  each  tooth,  or  its 
lobes,  and  point  to  the  character  of  the  changes  which  occur. 
This  has  occasionally  led  to  the  mention  of  abnormal  form.s. 

The  reader  will  find  scattered  through  the  work  some 
hints  with  regard  to  the  practical  bearing  of  anatomical  points 
on  operative  procedures,  which,  it  is  hoped,  will  be  of  value. 


PREFACE  TO  THE  SECOND  EDITION. 


THE  rapid  sale  of  the  first  edition  of  this  work  has  shown 
an  appreciation  of  a  need  for  a  more  complete  anatom- 
ical description  of  the  human  teeth.  In  preparing  the 
work  for  a  second  edition,  the  aim  has  been  to  render 
the  original  design  more  complete  in  its  details,  and  to  make 
such  verbal  alterations  as  would  better  fit  it  for  the  text-book 
for  the  college,  and  for  reference  by  the  practitioner.  The 
most  notable  changes  are  in  the  section  on  nomenclature ;  and 
these  are  confined  to  additional  explanations  of  words  and 
phrases.  For  the  convenience  of  students  a  brief  glossary  has 
been  added. 

A  number  of  the  illustrations  have  been  redrawn,  and  one 
has  been  added.  Some  of  the  numbers  of  the  illustrations  have 
been  changed  to  render  them  consecutive ;  but  the  numbering 
of  the  paragraphs  remains  unchanged.  Important  words,  espe- 
cially the  subjects  of  paragraphs  and  technical  words  the  first 
time  used,  have  been  printed  in  bold-faced  type.  This,  it  is 
hoped,  will  be  of  advantage  to  the  student  and  especially  con- 
venient for  reference. 

Valuable  aid  in  the  preparation  of  the  work  for  reissue  has 
been  rendered  by  Mr.  I.  W.  Davenport,  Drs.  D.  M,  Cattell, 
Edmund  Noyes,  and  C.  N.  Johnson.  G.  V.  B. 

Jacksonville,  III.,  July  15th,  i8gi. 


PREFACE  TO  THE  THIRD  EDITION. 


THE  continued  favor  with  which  this  work  is  received  by 
the  profession  has  made  another  edition  necessary.  In 
preparing  this  the  endeavor  has  been  to  improve  the 
detail  without  changing  the  form.  The  principal  changes 
will  be  found  in  the  nomenclature.  The  steady  progress  of 
dental  nomenclature  toward  more  exact  forms  demands  this. 
It  must  now  be  recognized  that  we  have  two  distinct  forms  of 
dental  nomenclature,  the  one  used  in  comparative  dental  anat- 
omy, the  other  in  human  dental  anatomy  for  the  purposes  of 
dentistry.  The  one  is  adapted  to  the  description  of  the  teeth  of 
the  various  animals,  including  the  teeth  of  man  when  his  teeth 
are  treated  of  in  the  comparative  sense ;  the  other  is  suited  to 
the  teeth  of  man  when  the  more  exact  and  detailed  descriptions 
necessary  to  operative  dentistry  are  presented.  These  word- 
forms  necessarily  become  the  basis  of  much  of  the  nomencla- 
ture of  operative  dentistry.  An  extended  examination  of  dental 
literature  shows  that  up  to  a  recent  period,  writers  on  operative 
dentistry  had  named  more  than  twice  as  many  points  on  the 
teeth  than  had  writers  on  dental  anatomy.  This  fact  shows  the 
necessity  that  had  existed  for  the  more  extended  and  systema- 
tized presentation  of  the  subject  of  dental  anatomy,  and  the 
closer  systematization  of  its  nomenclature.  However,  the 
reader  will  find  the  changes  introduced  limited  to  one  new  word, 
axial;  two  new  word-forms,  occlusal  in  place  of  occluding, 
and  incisal  in  compound  forms,  and  the  completion  of  the  sys- 
tematization of  the  names  of  the  angles  of  the  teeth.  This 
latter  has  required  but  few  word  changes  in  the  text. 

Improvement  has  also  been  made  in  some  of  the  descrip- 
tions, and  a  number  of  new  illustrations  have  been  added. 

G.  V.  B. 

Jacksonville,  III.,  August  21st,  1894. 


PREFACE  TO  THE  FOURTH  EDITION. 


ON  account  of  the  exhaustion  of  the  very  large  third 
edition  of  this  work  a  fourth  has  become  necessary. 
The    teacher    and    the    student    will    find    but    few 
changes.    The  author  takes  pride  in  referring  to  the 
very  general  approval  of  the  work  as  a  text-book,  and  to  the 
fact  that  teachers  who  have  used  it  in  their  classes  since  the 
first  edition  have  so  few  changes  to  suggest. 

The  changes  in  this  edition  consist  in  the  introduction  of 
tables  of  the  angles  of  teeth  and  the  angles  of  surfaces  of  teeth, 
intended  to  aid  the  student  in  fixing  these  in  his  mind,  and  in 
the  introduction  of  the  word  embrasure  as  an  additional  techni- 
cal term.  "^ 

Those  openings  between  the  angles  of  the  teeth  formed  by 
the  rounding  of  the  proximate  surfaces  toward  the  buccal  on 
the  one  side  of  the  proximate  contact  and  toward  the  lingual 
upon  the  other  have  never  had  a  specific  name,  and  the  word 
embrasure  has  been  introduced  to  supply  this  need  in  nomen- 
clature. The  word,  when  traced  to  its  derivation,  means  an 
opening  that  widens,  as  in  a  wall,  whether  outward  or  inward. 
It  has  been  most  used  in  connection  with  defensive  works ;  as 
"embrasures  for  cannon"  in  the  walls  of  forts ;  though  it  fre- 
quently occurs  in  descriptions  of  other  structures.  The  gen- 
eral progress  of  dental  nomenclature  toward  exactness  is  very 
gratifying,  and  it  is  hoped  that  the  addition  of  this  word  will  be 
found  advantageous.  G.  V.  B. 

Chicago,  October  gth.  1807 


GLOSSARY 


Alveolus.  (PI.  Alveoli.)  A  socket:  The  cavity  in  the 
process  of  the  maxillary  bone  in  which  the  root  of  a  tooth  is 
fixed. 

Alveolar  process.  The  projection  of  the  maxillary 
bones  which  envelops  the  roots  of  the  teeth  and  forms  their 
alveoli. 

Angle.  The  line,  or  point,  where  two  or  more  surfaces 
of  the  teeth  join.  The  mesial  and  buccal  surfaces  join  in  the 
formation  of  the  mesio-buccal  angle.     (See  Par.  7.) 

Apex.     The  terminal  end  of  the  root  of  a  tooth. 

Apical  foramen.  The  minute  opening  of  the  pulp  canal 
at  the  apex  of  the  root  of  a  tooth.     (See  Par.  153.) 

Apical  space.  The  space  between  the  bone,  or  wall  of 
the  alveolus,  and  the  apex  of  the  root  of  a  tooth.  This  space 
is  filled  with  the  soft  tissues  of  the  peridental  membrane,  and  is 
the  seat  of  alveolar  abscess. 

Axial  angle.  The  line  angles  that  are  parallel  with  the 
long  axes  of  the  teeth  are  called  axial  angles.  They  are  the 
mesio-buccal,  and  mesio-labial.  disto-buccal,  and  disto-labial, 
mesio-lingual  and  disto-lingual  angles. 

Axial  surfaces.  Those  surfaces  of  the  teeth  that  are 
parallel  with  their  long  axes.  They  are  labial,  buccal,  lingual, 
mesial,  and  distal  surfaces. 

Axial  walls.  Of  pulp  chambers.  Those  walls  that  are 
parallel  with  the  long  axes  of  the  teeth ;  the  mesial,  distal,  buc- 
cal, and  lingual  walls. 

Bell-crowned.  A  tooth  in  which  the  mesio-distal  diam- 
eter of  the  crown  is  much  greater  than  that  of  the  neck. 


GLOSSARY. 


Bicuspid.  A  tooth  with  two  cusps.  They  are  also  called 
pre-molars.  There  are  eight  bicuspids  ;  two  on  each  side  of  the 
upper  jaw,  and  two  on  either  side  of  the  low^er  jaw.  They  are 
named  right  and  left  upper  first  and  second,  and  right  and  left 
lower  first  and  second  bicuspids.  They  are  situated  between 
the  cuspids  and  molars. 

Border  of  the  alveolar  process.  The  thin  edge  of 
the  alveolar  process  surrounding  the  necks  of  the  teeth. 

Buccal.     Pertaining  to  the  cheek.    Toward  the  cheek. 

Buccal  surface.  The  surface  of  a  tooth  next  to  the 
cheek. 

Buccal-gingival  ridge.  A  prominent  ridge  near  the 
gingival  line  on  the  buccal  surface  of  the  deciduous  molars.  It 
is  especially  prominent  on  the  first  deciduous  molars. 

Bucco-lingual.  From  the  cheek  toward  the  tongue;  as 
the  bucco-lingual  diameter  of  the  crown  of  a  lower  first  molar. 

Canal.     See  Root  Canal. 

Cementum.  A  tissue  resembling  bone  which  forms  the 
outer  surface  of  the  roots  of  the  teeth. 

Contact  point.  The  point  on  the  proximate  surface  of 
a  tooth  which  touches  a  neighboring  tooth. 

Crown.  That  portion  of  a  tooth  which  is  covered  with 
enamel,  and  which  projects  from  the  tissues  in  which  the  root 
is  fixed. 

Cutting  edge.  The  edge  formed  by  the  junction  of  the 
labial  and  lingual  surfaces  of  the  incisor  and  cuspid  teeth.  In 
the  cuspids  the  edge  is  raised  to  a  point  near  its  center. 

Cusp.  A  pronounced  elevation,  or  point,  on  the  surface 
of  a  tooth,  more  especially  on  the  occlusal  surface. 

Cuspid.  A  tooth  with  one  point,  or  cusp.  There  are 
four  cuspids:  one  on  either  side  in  each  jaw,  situated  at  the 
corners  of  the  mouth. 

Deciduous  teeth.  The  teeth  of  the  child  which  are 
shed  to  give  place  to  the  permanent  teeth.  They  are  also  called 
temporary  teeth. 

Dentine.  The  tissue  of  which  the  main  body  of  a  tooth 
is  formed. 


GLOSSARY. 


Developmental  grooves.  Fine  depressed  lines  in  the 
enamel  of  a  tooth  which  mark  the  junction  of  its  lobes.  (See 
Pars.  21  and  69.) 

Developmental  lines.     See  developmental  grooves. 

Distal.  Away  from  the  median  line  of  the  face  follow- 
ing the  curve  of  the  dental  arch.  The  surface  of  a  tooth  most 
distant  from  the  median  line.     (See  Par.  5.) 

Distally.  A  direction  away  from  the  median  line  of  the 
face  following  the  curve  of  the  dental  arch. 

Distal  angle.  A  contraction  of  disto-incisal  angle. 
Used,  also,  instead  of  disto-bucco-occlusal  angle   {q.  v.). 

Disto-buccal  angle.  The  angle  formed  by  the  union 
of  the  distal  and  buccal  surfaces  of  the  bicuspids  and  molars. 

Disto-bucco-occlusal  angle.  The  angle  or  corner  of 
a  bicuspid  or  molar  tooth  formed  by  the  junction  of  the  angles 
of  its  distal,  buccal,  and  occlusal  surfaces  at  a  point. 

Disto-incisal  angle.  The  angle  or  corner  of  an  incisor 
or  cuspid  tooth  formed  by  the  jvmction  of  the  distal  surface  and 
cutting  edge,  or  incisal  surface. 

Disto -labial  angle.  The  angle  formed  by  the  union  of 
the  distal  and  labial  surfaces  of  the  incisors  and  cuspids. 

Disto-lingual  angle.  The  angle  formed  by  the  union  of 
the  distal  and  lingual  surfaces  of  any  of  the  teeth. 

Disto-linguo-occlusal  angle.  The  angle  or  corner  of 
a  bicuspid  or  molar  tooth  formed  by  the  junction  of  the  angles 
of  its  distal,  lingual,  and  occlusal  surfaces  at  a  point.  Rarely 
used. 

Disto-occlusal  angle.  The  angle  formed  by  the  union 
of  the  distal  and  occlusal  surfaces  of  the  bicuspids  and  molars. 

Embrasure.  An  opening  that  widens  outward  or  in- 
ward ;  as  an  opening  in  a  wall  for  cannon.  That  portion  of  the 
inter-proximate  space  that  widens  toward  the  buccal  or  labial, 
or  toward  the  lingual. 

Enamel.  A  very  hard  tissue  covering  the  crown  of  a 
tooth. 

Fissure.      A  fault  in  the  surface  of  a  tooth  caused  by 


GLOSSARY. 


the   imperfect  joining   of   the   enamel   of  the   different   lobes. 
Fissures  occur  along  the  lines  of  the  developmental  grooves. 
>  /  Fossa.       (PI.  Fossae.)     A  round  or  angular  depression  in 

the  surface  of  a  tooth.    Fossae  occur  mostly  in  the  occlusal  sur- 
faces of  the  molars,  and  in  the  lingual  surfaces  of  the  incisors. 

Gingiva.  (PI.  Gingivae.)  The  portion  of  gum  tissue 
enveloping  the  necks  of  the  teeth  crown-wise  from  the  attach- 
ment at  the  gingival  line.    The  free  margin  of  the  giim. 

Gingival.  Pertaining  to  the  gingival  line;  as  the  curva- 
ture of  the  gingival  line,  gingival  margin,  etc. 

Gingival  curvature.  The  deviation  of  the  gingival  line 
from  the  horizontal  in  its  course  around  the  neck  of  a  tooth. 

Gingival  line.  The  line  around  the  neck  of  a  tooth  at 
which  the  gingiva  is  attached.  The  line  of  junction  of  the 
enamel  and  cementum. 

Gingival  margin.  The  portion  of  the  crown  of  a  tooth 
next  to  the  gingival  line. 

Gingivally.  A  direction  from  any  part  of  the  crown 
toward  the  gingival  line  of  the  tooth. 

Groove.  A  long-shaped  depression  in  the  surface  of  a 
tooth.     (See  Par.  ii.) 

Horn.  A  slender,  or  blunt  pointed  process  of  the  pulp 
of  a  tooth  extending  toward  the  point  of  a  cusp. 

Incisal.  The  cutting  edges  of  the  incisors  and  cuspids 
are  regarded  as  incisal  surfaces. 

Incisal  margin.  That  margin  of  a  surface  of  an  incisor 
or  a  cuspid  tooth  formed  by  the  incisal  surface  or  cutting  edge ; 
as  the  incisal  margin  of  the  labial  surface  of  the  central  incisor. 

Incisor.  A  tooth  with  a  cutting  edge.  There  are  four 
incisors  in  the  upper  jaw,  and  four  in  the'lower  jaw.  They  are 
called  the  upper  and  lower  right  and  left  central,  and  the  upper 
and  lower  right  and  left  lateral,  incisors. 

Inclination.  Of  a  tooth  :  The  deviation  of  the  long  axis 
of  a  tooth  from  the  perpendicular  line ;  as  the  mesial  inclination 


GLOSSARY.  Xlir 

of  the  incisors.  (See  Par.  191.)  Of  a  surface:  The  deviation 
of  a  portion  of  the  surface  of  a  tooth  from  the  general  plane  of 
that  surface. 

Incline.       See  Inclination. 

Inter-proximate  embrasure.  That  portion  of  the  inter- 
proximate  space  which  widens  toward  the  buccal  or  labial,  or 
toward  the  lingual.     (See  Par.  194.) 

Inter-proximate  space.  The  V-shaped  space  bounded 
by  the  proximate  surfaces  of  adjoining  teeth,  and  the  border  of 
the  septum  of  the  alveolar  process  between  their  necks.  Nor- 
mally this  space  is  filled  with  gum  tissue.     (See  Par.  193.) 

Labial.      Pertaining  to  the  lips.    Toward  the  lips. 

Labial  surface.  The  surface  of  a  tooth  next  to  the  lips. 
The  incisors  and  cuspids  have  labial  surfaces. 

Labially.    A  direction  toward  the  lips. 

Labio-lingual.  From  the  lips  toward  the  tongue;  as 
the  labio-lingual  diameter  of  the  central  incisor. 

Labio-lingually.  A  direction  from  the  lips  toward  the 
tongue. 

Line  angles.  Of  the  teeth :  Those  angles  formed  by 
the  junction  of  two  surfaces  along  a  line;  as  the  mesio-buccal 
angle,  disto-buccal  angle,  etc. 

Lingual.  Next  to,  or  toward  the  tongue;  as  lingual 
surface. 

Lingually.     A  direction  toward  the  tongue. 

Lingual  surface.  A  surface  of  a  tooth  next  to  the 
tongue.    All  of  the  teeth  have  lingual  surfaces. 

Linguo-gingival  fissure.  A  fissure  occurring  occa- 
sionally in  the  lingual  surface  of  the  upper  incisors.  It  usually 
separates  the  lingual  lobe  from  one  of  the  marginal  ridges  and 
extends  into  the  cemehtum.     (See  Fig.  10.) 

Linguo-gingival  ridge.  A  ridge  near  the  gum  on  the 
lingual  surface  of  the  incisors  and  cuspids.  It  is  on  the  lingual 
lobe.     (See  Par.  21.) 

Lobe.  A  division  of  a  tooth  formed  from  a  separate 
^        point  of  the  beginning  of  calcification.     (See  Pars.  21  and  69.) 


XIV  GLOSSARY. 

Mammelons.  The  three  rounded  prominences  seen  on 
the  cutting  edges  of  the  incisors  when  they  first  come  through 
the  gums.     (E.  Magitot.) 

Marginal  ridge.  The  ridges,  or  elevations  of  enamel 
on  the  margins  of  the  occlusal  surface  of  the  bicuspids  and 
molars,  and  on  the  mesial  and  distal  margins  of  the  lingual 
surface  of  the  incisors  and  cuspids. 

Median  line.  The  antero-posterior  perpendicular  cen- 
tral line  of  the  body. 

Mesial.  Toward  the  median  line.  Those  surfaces  of  the 
teeth  which,  as  they  stand  in  the  arch,  and  following  its  curve, 
are  toward  the  median  line,  are  called  mesial  surfaces. 

Mesial  angle.  A  contraction  of  mesio-incisal  angle,  also 
of  mesio-bucco-occlusal  angle  {q.  v.). 

Mesially.      Toward  the  median  line. 

Mesio-buccal  angle.  The  angle  formed  by  the  union  of 
the  mesial  and  buccal  surfaces  of  the  bicuspids  and  molars. 

Mesio-bucco-occlusal  angle.  The  angle  or  corner 
formed  by  the  junction  at  a  point  of  the  angles  of  the  mesial, 
buccal,  and  occlusal  surfaces  of  the  bicuspids  and  molars. 

Mesio-distal.  From  mesial  to  distal;  as,  the  mesio- 
distal  diameter  of  the  lower  first  molar. 

Mesio-incisal  angle.  The  angle  or  corner  formed  by 
the  junction  of  the  mesial  surface  and  cutting  edge,  or  incisal 
surface,  in  the  incisors  and  cuspids. 

Mesio-labial  angle.  The  angle  formed  by  the  union  of 
the  mesial  and  labial  surfaces  of  the  incisors  and  cuspids. 

Mesio-lingual  angle.  The  angle  formed  by  the  union 
of  the  mesial  and  lingual  surfaces  of  the  teeth. 

Mesio-lingual  groove.  A  developmental  groove  run- 
ning from  the  mesial  surface  diagonally  to  the  lingual  surface 
in  upper  first  molars  that  have  the  fifth  cusp.     (See  Par.  69.) 

Mesio-linguo-occlusal  angle.  The  angle  or  corner 
formed  by  the  junction  of  the  angles  of  the  mesial,  lingual,  and 
occlusal  surfaces  of  the  bicuspids  and  molars.    Rarely  used. 


GLOSSARY.  XV 

Mesio-occlusal  angle.  The  angle  formed  by  the  union 
of  the  mesial  and  occlusal  surfaces  of  the  bicuspids  and  molars. 

Neck.  That  portion  of  the  tooth  which  forms  the  junc- 
tion of  the  crown  and  root. 

Oblique  ridge.  A  ridge  running  obliquely  across  the 
occlusal  surface  of  the  upper  molars.  It  is  formed  by  the 
union  of  the  triangular  ridge  of  the  disto-buccal  cusp  with  the 
distal  portion  of  the  ridge  forming  the  mesio-lingual  cusp. 

'Occlude.     To  shut.    To  close. 

Occlusal  surface.  That  surface  of  a  bicuspid  or  molar 
tooth  that  makes  contact  with  a  tooth  of  the  opposite  jaw  when 
the  mouth  is  closed. 

Permanent  teeth.  The  teeth  of  adult  age  as  distin- 
guished from  the  temporary,  or  deciduous  teeth. 

Pit.    A   sharp,   pointed   depression   in  the   enamel.      Pits 
occur  mostly  where  several  developmental  grooves  join;  as  in 
the  occlusal  surfaces  of  the  molars,  and  at  the  endings  of  the 
^  buccal  grooves  on  the  buccal  surfaces  of  the  molars. 
/  ^  Point  angles.     Of  the  teeth :  Those  corners  or  angles 

formed  by  the  junction  of  the  angles  of  three  surfaces  at  a 
point;  as  the  disto-bucco-occlusal  angle,  the  mesio-bucco- 
occlusal  angle,  etc. 

Point  of  proximate  contact.  The  point  at  which  the 
proximate  surface  of  a  tooth  touches  the  proximate  surface  of 
a  neighboring  tooth. 

Proximate  contact.  The  contact,  or  touching-,  of  the 
proximate  surfaces  of  neighboring  teeth. 

Proximation.  The  near  approach,  or  contact,  of  the 
proximate  surfaces  of  neighboring  teeth. 

Proximate  surface.  The  surface  of  a  tooth  which  lies 
next  to  another  tooth.     (See  Par.  5.) 

Pulp.  The  soft  tissue  that  fills  the  pulp  chambers  and 
root  canals  of  the  teeth. 

Ridge.    A  long-shaped  elevation  on  the  surface  of  a  tooth. 

Root.  That  portion  of  the  tooth  that  is  fixed  in  the  bony 
walls  of  the  alveolus,  or  socket ;  and  is  covered  with  cementum. 


XVI  GLOSSARY. 

Root  canal.  The  opening  through  the  center  of  the 
long  axis  of  the  root  of  a  tooth  from  the  crown  to  the  apex. 

Rugae.  A  series  of  irregular  ridges  in  the  roof  of  the 
mouth. 

Septum.  (PI.  Septa.)  A  partition  :  That  portion  of  ths 
alveolar  process  which  lies  between  the  roots  of  the  teeth  sepa- 
.  rating  their  alveoli. 

Succedaneous  teeth.  Those  of  the  permanent  teeth 
which  succeed,  or  take  the  places  of,  the  temporary  teeth. 

Sulcate  groove.  A  groove  following  the  bottom  of  a 
1/      sulcus. 

Sulcus.  (PI.  Sulci.)  A  notable  long-shaped  depression 
in  the  surface  of  a  tooth  the  inclines  of  which  meet  at  an  angle. 
A  sulcus  has  a  developmental  groove  at  the  junction  of  its 
inclines. 

Supplemental  groove.  "A  shallow  long-shaped  depres- 
sion in  the  surface  of  a  tooth,  generally  with  a  smoothly 
rounded  bottom.  Supplemental  grooves  differ  from  develop- 
mental grooves  in  that  they  do  not  mark  the  junction  of  lobes. 

Supplemental  lobe.  A  lobe  that  does  not  belong  to  the 
typical  form  of  the  tooth ;  an  additional  lobe. 

Supplemental  ridge.  A  ridge  on  the  surface  of  a  tooth 
that  does  not  belong  to  the  typical  form  of  the  tooth ;  and  addi- 
tional ridge. 

Temporary  teeth.      See  deciduous  teeth. 

Thick-necked.  A  tooth  in  which  the  mesio-distal  diam- 
eter of  the  neck  is  nearly  equal  to  that  of  the  crown.  (See  bell- 
crown.  ) 

Thirds.  Division  of  a  crown  of  a  tooth;  as  to  length, 
into  occlusal,  or  incisal  third,  middle  third,  and  gingival  third; 
as  to  mesio-distal  breadth,  into  mesial  third,  middle  third,  and 
distal  third. 

Transverse  ridge.  A  ridge  formed  of  two  triangular 
ridges,  which  join  to  form  a  continuous  ridge  across  the  oc- 
clusal surface  of  a  tooth. 


GLOSSARY.  Xvii 

Triangular  ridge.  A  ridge  running  from  the  point  of  a 
cusp  toward  the  central  portion  of  the  occlusal  surface  of  a 
tooth. 

Tubercle.  A  slight  rounded  elevation  on  the  surface  of  a 
tooth.  Tubercles  occur  frequently  on  the  linguo-gingival  ridge 
of  the  incisors,  and  occasionally  upon  various  parts  of  other 
teeth.    They  are  deviations  from  the  typical  tooth  forms. 


DENTAL   ANATOMY. 

XOMENCLATURE. 

1.  Man's  food  is  both  animal  and  vegetable,  and  his 
teeth  are  so  formed  as  to  enable  him  to  readily  masticate  either 
kind ;  therefore,  his  teeth  differ  from  those  of  both  the  carnivor- 
ous and  herbivorous  animals,  and  form  the  type  of  the  om- 
nivora.  They  are  formed  for  cutting,  tearing,  and  comminut- 
ing many  kinds  of  food.  The  incisors,  situated  anteriorly, 
have  edges  for  cutting;  the  cuspids  and  bicuspids, at  the  an- 
gles of  the  mouth,  have  fairly  sharp,  though  not  very  long, 
points  or  cusps,  suited  for  tearing;  while  the  molars,  situated 
in  the  posterior  part  of  the  mouth,  have  broad,  tuberculated 
surfaces,  which  serve  well  to  grind  or  comminute  the  more 
solid  masses.  The  forms  of  the  teeth  of  man  indicate  a  design 
that  his  food  should  be  taken  in  rather  small  masses,  consid- 
ered -from  the  standpoint  of  the  habits  of  animals  in  general, 
and  that  it  should  be  very  thoroughly  commingled  with  saliva 
before  being  passed  to  the  stomach. 

2.  The  adult  has  thirty-two  teeth :  four  incisors,  two 
cuspids,  four  bicuspids,  and  six  molars  in  each  jaw.  Scientific 
men  express  the  denomination  and  number  of  the  teeth  of  the 
mammalia  by  formulae,  in  which  the  denomination  is  repre- 
sented by  the  initial  letter,  followed  by  a  horizontal  line,  with 
the  number  of  that  kind  of  teeth  on  one  side  of  the  upper  jaw 
written  above  the  line,  and  the  number  in  the  lower  jaw  written 
below  the  line.    The  dental  formula  of  man  is  written  thus : 

I  I  C  i  B  f  M  I  =  32. 

This  formula  is  read  thus :    Incisors,  two  upper  and  two  lower ; 
cuspids,  one  upper  and  one  lower ;  bicuspids,  two  upper  and 


NOMENCLATURE. 


two  lower ;  molars,  three  upper  and  three  lower ;  sixteen  on 
one  side.  As  the  opposite  side  has  the  same,  the  full  number 
is  thirty-two.  The  teeth  are  composed  of  four  tissues :  Enamel, 
which  covers  the  crown ;  dentine,  which  forms  the  body  of 
both  crown  and  root;  cementum,  which  covers  the  root  and 
joins  with  the  enamel  at  the  gingival  line,  or  neck  of  the  tooth; 
and  pulp  tissue  which  fills  the  central  cavity  of  the  dentine. 

3.  Each  tooth  presents  for  description  certain  characters 
common  to  all,  such  as  crown,  neck  or  gingival  line,  root,  pulp- 
chamber,  canal,  and  surfaces  of  crown  and  root.  The  crown 
of  a  tooth  is  that  part  which  projects  beyond  the  gum  tissue, 
and  is  covered  with  enamel;  while  the  root,  covered  with  ce- 
mentum, is  that  portion  fixed  in  the  bony  process  of  the  jaw, 
by  which  the  whole  tooth  is  held  securely  in  position.  The 
root  of  a  tooth  may  be  single,  as  in  the  incisors  and  cuspids; 
divided  into  two  roots  as  in  the  lower  molars ;  or  into  three 
roots,  as  in  the  upper  molars ;  or  into  a  greater  number,  as  in 
exceptional  examples.  The  root  is  divided  into  the  body,  or 
main  portion;  the  Apex,  or  terminal  end  of  a  root;  and  the 
neck,  which  marks  the  junction  of  the  root  with  the  crown. 
A  tooth  is  also  marked  with  a  slight  constriction  at  the  neck, 
and  by  the  junction  of  the  enamel  with  the  cementum.  The 
latter,  which  forms  a  visible  line  encircling  the  tooth,  is  called 
the  gingival  line.  It  is  so  curved  in  its  course  as  to  present 
a  convexity  toward  the  crown  on  the  proximate  surfaces,  to 
correspond  with  the  line  of  the  gum  as  it  passes  over  the  alveo- 
lar ridge  from  the  labial  to  the  lingual  side  of  the  arch.  On 
the  anterior  teeth,  it  is  also  so  curved  in  passing  the  labial  and 
lingual  surfaces  as  to  present  a  concavity  toward  the  crown. 
These  are  called  the  curvatures  of  the  gingival  line,  or  the 
gingival  curvature.  The  neck  of  a  tooth  is  common  to  all 
of  the  roots,  whatever  the  number,  for  the  point  of  division  into 
two  or  more  roots  is  always  rootward  from  the  neck. 

4.  The  crowns  of  the  incisors  and  cuspids  present  for 
examination  four  surfaces  and  an  edge ;  and  the  crowns  of  the 


NOMENCLATURE. 


bicuspids  and  molars,  five  surfaces.  (Diagram  A.)  These 
surfaces  are  named  according  to  their  position  and  use.  Those 
of  the  incisors  and  cuspids  presenting  toward  the  Hps,  are 
called  labial  surfaces ;  those  of  the  bicuspids  and  molars  pre- 
senting toward  the  cheek,  buccal  surfaces  ;  all  presenting 
toward  the  tongue,  lingual  surfaces,  whether  in  the  upper  or 
the  lower  jaw.*  Those  surfaces  which  come  in  contact  with 
the  opposing  teeth  in  closing  the  mouth  are  called  occlusal 
surfaces.  These  surfaces  of  the  bicuspids  and  molars  are  also 
called  grinding  surfaces. 

5.  The  surfaces  of  the  teeth  that  present  toward,  or  lie 
against,  adjoining  teeth  are  called  proximate  or  proximal, 
surfaces.  The  proximate  surfaces  are  also  more  closely  de- 
fined by  the  terms  mesial  and  distal.  These  terms  have  spe- 
cial reference  to  the  position  of  the  surface  relative  to  the  cen- 
tral or  the  median  line  of  the  face.  This  line  is  drawn  along, 
the  suture  uniting  the  superior  maxillary  bones,  or  perpendic- 
ularly through  the  center  of  the  face  and  mouth,  and  passes 
between  the  central  incisors  of  both  the  upper  and  lower  jaws. 
Those  proximate  surfaces  which,  as  they  are  placed  in  the  arch, 
and  follozving  its  curve,  are  toward  the  median  line,  are  called 
mesial  surfaces ;  and  those  most  distant  from  the  median 
line  are  called  distal  surfaces.  The  mesial  surfaces  of  the 
central  incisors,  both  upper  and  lower,  proximate  each  other; 
but  in  all  other  cases  a  mesial  surface  proximates  a  distal. 
Also,  a  distal  surface  always  proximates  a  mesial  surface, 
except  those  of  the  third  molars,  upper  and  lower,  which  have 
no  distal  proximating  teeth.  The  points  at  which  the  proxi- 
mate surfaces  touch  each  other  as  the  teeth  stand  in  the  line  of 
the  arch,  are  called  the  points  of  proximate  contact,  or  sim- 
ply contact  points. 

For  convenience  in  designating  the  different  parts  of  the 
crowns  of  the  teeth,  they  may  be  divided  into  thirds,  in  any 

*  Some  authors  use  the  term  "palatine  surfaces"  for  those  of  the 
upper  jaw,  and  "lingual"  for  those  of  the  lower.  This  seems  unneces- 
sary. 


NOMENCLATURE. 


one  of  .three  directions  :  Inciso-  or  occluso-gingivally  into  incisal, 
or  occlusal  third,  middle  third,  and  gingival  third,'^mesio-dis- 
tally  into  the  mesial  third,  middle  third,  and  distal  third ;  bucco- 
lingually  into  the  buccal  third,  middle  third,  and  lingual  third. 

Each  of  the  five  surfaces  may  be  divided  into  thirds  in 
either  one  of  two  directions.  The  labial,  or  buccal,  and  the 
lingual  surfaces  are  divided  inciso-  or  occluso-gingivally,  into 
the  incisal,  or  occlusal  third,  middle  third,  and  gingival  third ; 
mesio-distally  into  the  mesial  third,  middle  third,  and  distal 
third.  Mesial  and  distal  surfaces  are  divided  inciso-  or  oc- 
cluso-gingivally into  the  incisal,  or  occlusal  third,  middle  third, 
and  gingival  third ;  bucco-lingually,  into  the  buccal  third,  mid- 
dle third,  and  lingual  third.  The  occlusal  surfaces  are  divided 
'mesio-distally  into  the  mesial  third,  middle  third,  and  distal 
third ;  bucco-lingually,  into  the  buccal  third,  middle  third,  and 
lingual  third.  The  cutting  edges,  or  incisal  surfaces  of  the 
incisors  and  cuspids,  are  divided  mesio-distally  only.  These 
divisions  are  the  mesial  third,  middle  third,  and  distal  third. 

6.  The  incisors  present  a  cutting  edge  by  the  junction 
of  the  labial  and  lingual  surfaces  along  a  line.  In  the  cuspids, 
this  joining  of  the  surfaces  to  form  an  edge  is  raised  to  a  point 
near  the  center  of  its  length,  forming  a  cusp,  hence  the  term 
cuspid,  a  tooth  with  one  point.  The  cutting  edges  of  the  in- 
cisors, and  the  occlusal  surfaces  of  the  bicuspids  and  molars, 
come  in  contact  with  the  similar  surfaces  of  the  teeth  of  the 
opposing  jaw  when  the  mouth  is  closed,  as  in  the  act  of  biting. 
The  incisors  and  cuspids  of  the  upper  jaw  do  not  occlude  ex- 
actly on  the  cutting  edges  or  cusps,  but  generally  just  back  of 
them ;  though  for  convenience,  the  term  occlusal  may  be  ap- 
plied to  them  as  if  they  did,  though  they  will  generally  be  called 
cutting  edges,  and  the  adjective  form  incisal  will  be  used 
in  all  compound  words.  The  occlusal  surfaces  of  the  bicuspids 
have  two  cusps,  hence  the  term  bicuspid,  a  tooth  with  two 
points ;  and  the  occlusal  surfaces  of  the  molars  have  four  cusps 
and  sometimes  more. 


NOMENCLATURE. 


7.  The  angles  of  the  teeth  are  of  two  kinds :  Line 
angles  and  point  angles.  The  line  angles  are  formed  by  the 
junction  of  two  surfaces  along  a  line.  The  point  angles  are 
formed  by  the  junction  of  three  surfaces  forming  a  corner.  The 
incisors  and  cuspids  have  four,  and  the  bicuspids  and  molars 
have  eight  line  angles.  Angles  are  named  by  combining  in  a 
compound  word  the  names  of  the  surfaces  which  join  to  form 
the  angle.  The  incisors  and  cuspids  have  mesio-labial  angles, 
which  extend  from  the  cutting  edge  to  the  gingival  line  along 
the  line  of  union  of  the  mesial  and  labial  surfaces.  Also, 
disto-labial  angles,  mesio-lingual  angles,  and  disto-lingual 
angles,  formed  similarly  by  the  junction  of  the  surfaces  named 
in  these  compound  words. 

The  bicuspids  and  molars  have  mesio-buccal  angles, 
formed  by  the  junction  of  the  mesial  and  buccal  surfaces  along 
a  line  from  the  occlusal  surface  to  the  gingival  line.  Also, 
disto-buccal  angles,  mesio-lingual  angles,  and  disto-lingual 
angles,  all  of  which  are  formed  in  the  same  manner  as  the 
mesio-buccal.  These  are  called  the  axial  line  angles  because 
they  are  parallel  with  the  long  axes  of  the  teeth. 

The  bicuspids  and  molars  have  also  four  occlusal  line  an- 
gles,' which  are,  however,  more  generally  called  marginal 
ridges.  The  mesio-occlusal  angles  extend  bucco-lingually 
along  the  line  of  junction  of  the  mesial  and  occlusal  surfaces. 
The  disto-occlusal  angles  are  similarly  formed.  The  bucco- 
occlusal  angles  and  the  linguo-occlusal  angles  extend  mesio- 
distally  along  the  line  of  junction  of  the  surfaces  named  in 
these  compound  words. 

The  point  angles  of  the  bicuspids  and  molars  are  four 
occlusal  and  four  gingival.  As  these  are  formed  by  the  junc- 
tion of  the  angles  of  three  surfaces  forming  a  corner,  their 
names  are  compounds  of  the  names  of  the  three  uniting  sur- 
faces. The  mesio-bucco-occlusal  angles  are  formed  by  the 
junction  of  the  angles  of  these  three  surfaces  at  a  point.  The 
mesio-linguo-occlusal  angles,  the  disto-bucco-occlusal 
angles,  and  the  disto-linguo-occlusal  angles  are  formed  in  a 


NOMENCLATURE. 


V 


similar  manner.    These  names  of  point  angles  are  precisely  the 
same  for  all  of  the  bicuspid  and  molar  teeth. 

The  incisors  and  cuspids  have,  on  account  of  their  wedge- 
like form,  but  two  incisal  point  angles.  These  are  the  mesio- 
incisal  and  disto-incisal  angles,  which  form  the  corners  at 
the  mesial  and  distal  terminations  of  the  incisal  surface  or  cut- 
ting edge. 

The  gingival  point  angles  represent  the  corners  of  the 
crowns  of  the  teeth  at  their  junction  with  the  roots  at  the  gingi- 
val line,  or  the  gingival  termination  of  the  axial  line  angles ; 
and  are  named  precisely  as  the  axial  line  angles,  with  the  addi- 
tion of  the  word  gingival.  Thus,  the  incisors  and  cuspids 
have  mesio-labio-gingival  angles, mesio-linguo-gingival  an- 
gles, disto-labio-gingival  angles,  and  disto-linguo-gingival 
angles.  These  angles  are  named  in  the  same  way  for  the  bicus-. 
pids  and  molars,  except  that  the  word  buccal  is  substituted  for 
labial;  thus,  mesio-bucco-gingival  angle,  disto-bucco-gin- 
gival  angle,  the  angles  on  the  lingual  being  named  as  in  the 
incisors.  Up  to  the  present  time  the  gingival  point  angles  have 
not  been  used  in  descriptions  of  the  teeth,  and  are  given  here 
only  for  the  sake  of  completeness. 

When  any  individual  surface  of  a  tooth  is  considered  alone 
it  is  regarded  as  having  margins  and  angles  of  its  own,  or  be- 
longing to  it.  Each  margin  is  designated  by  the  name  of  the 
surface  with  which  it  is  joined,  except  that  toward  the  gingival 
line,  which  takes  the  name  gingival  margin.  The  buccal  sur- 
face of  a  bicuspid  or  molar  has  a  gingival  margin,  a  mesial 
margin,  a  distal  margin,  and  an  occlusal  margin.  The  labial 
surface  of  an  incisor  has  a  gingival  margin,  a  mesial 
margin,  a  distal  margin,  and  an  incisal  margin.  The  margins 
of  the  lingual  surfaces  of  all  of  the  teeth  are  named  in  precisely 
the  same  terms  as  those  of  their  buccal  or  labial  surfaces.  Also, 
the  margins  of  mesial  and  distal  surfaces  are  named  in  the  same 
terms.  A  mesial  or  distal  surface  of  a  bicuspid  or  molar  has  a 
gingival  margin,  a  buccal  margin,  a  lingual  margin,  and  an 
occlusal  margin.  The  mesial  and  distal  surfaces  of  the  incisors 


NOMENCLATURE. 


and  cuspids  have,  on  account  of  their  triangular  form,  only- 
three  margins:  the  gingival,  labial  and  lingual. 

The  angles  of  a  surface  of  a  tooth  are  named  by  com- 
bining the  names  of  the  margins  joining  to  form  the  angle. 
Thus,  the  buccal  surface  of  a  molar  has  four  angles,  the  mesio- 
occlusal,  disto-occlusal,  mesio-gingival  and  disto-gingi- 
val  angles.  All  angles  of  the  surfaces  of  the  teeth  are  named 
on  this  plan.  The  mesial  and  distal  surfaces  of  the  incisors  and 
cuspids  having  but  three  margins  have  but  three  angles:  the 
labio-gingival,  linguo-gingival,  and  incisal  angles.*  (The 
name  incisal  angle  is  an  exception  to  the  general  rule  for 
naming  angles  of  surfaces.) 

8.  A  cusp  is  a  pronounced  elevation,  more  or  less  pointed 
on  the  surface  of  a  tooth,  but  more  especially  on  the  occlusal 
surface.  A  slight  elevation  is  often  called  a  tubercle,  as  that 
frequently  seen  near  the  gum  on  the  lingual  surface  of  the 
upper  incisors.  These  are  generally  deviations  from  the  typi- 
cal forms  of  the  teeth. 

9.  Long-shaped  elevations  on  the  surfaces  of  teeth  are 
called  ridges,  and  are  named  according  to  their  location  or 
form;  as  buccal  ridge,  lingual  ridge,  and  marginal  ridge.  The 
marginal  ridges  are  those  elevations  of  the  enamel  which  form 
the  margins  of  the  occlusal  surfaces  of  the  bicuspids  and  mo- 
lars, and  the  mesial  and  distal  margins  of  the  lingual  surfaces  of 
the  incisors  and  cuspids.  Those  ridges  which  descend  from 
the  cusps  of  the  molars  and  bicuspids  toward  the  central  part  of 
the  occlusal  surfaces  are  called  triangular  ridges.  They  are 
so-called  because  the  typical  form  of  the  ridges  is  usually  that 

*  The  student  should  note  carefully  the  difiference  between  the 
names  of  the  angles  of  a  tooth  and  the  angles  of  a  surface  of  a  tooth. 
To  illustrate :  The  mesio-bucco-occlusal  angle  of  a  tooth  is  in  effect 
the  bucco-occlusal  angle  of  its  mesial  surface,  the  mesio-buccal  angle 
of  its  occlusal  surface,  or  the  mesio-occlusal  angle  of  its  buccal  sur- 
face. In  this  work  the  descriptions  are  mostly  of  individual  surfaces, 
hence  the  names  of  the  angles  of  surfaces  are  much  oftener  used  than 
the  names  of  the  angles  of  the  teeth. 


NOMENCLATURE. 


The  following  tables  of  the  angles  of  teeth  and  the  angles  of 
surfaces  of  teeth,  will  assist  the  student  in  obtaining  a  clear  under- 
standing of  them  if  studied  in  connection  with  the  text  and  the  illus- 
trations.* 


Angles  of  teeth  < 


Line  angles 


{Mesio-labial 
Disto-labial 
Mesio-lingual 
Disto-lingual 

Mesio-buccal 
Disto-buccal 
Mesio-lingual 
Disto-lingual 


Point  angles 


Bicuspids 
^  and  molars 


Incisors 
and  cuspids 

Bicuspids 
and  molars 


Mesio-occlusal 
Disto-occlusal 
Bucco-occlusal 
Linguo-occlusal 

Mesio-incisal 
Disto-incisal 

Mesio-bucco-occlusal 
Disto-bucco-occlusal 
Alesio-linguo-occlusal 
Disto-linguo-occlusal 


Angles  of 
the  surfaces 
of  teeth 


Incisors 
and  cuspids 


Labial  and  lingual 
surface  angles 


Mesial  and  distal 
surface  angles 


Bicuspids 
and  molars 


Mesio-incisal 
Disto-incisal 
Mesio-gingival 
Disto-gingival 

Labio-gingival 

Linguo-gingival 

Incisal 


{Alesio-occlusal 
Disto-occlusal 
Mesio-gingival 
Disto-gingival 

r  Mesio-buccal 
J  Disto-buccal 


Occlusal 
surface  angles 


I  Mesio-lingual 
I  Disto-lingual 


f  Bucco-occlusal 
Mesial  and  distal    J  Bucco-gingival 
surface  angles       ]  Lmguo-occlusal 
L  Linguo-gingival 


*  Suggested   by   Dr.    Wm.   E.    Harper. 


Note. — In  the  naming  of  the  surfaces  and  angles  of  the  teeth  the  crowns  are 
regarded  as  representing  cubes  with  the  angles  more  or  less  rounded,  though  they 
are  named  as  if  they  were  true  cubes.  For  this  reason  the  diagrams  here  given  for 
the  explanation  of  these  names  are  drawn  as  cubes. 

Diagram  A  ("Parg  \  find  5)- — The  Surfaces  of  a  Lower  Molar,  m,  Mesial 
surface;  /,  lingual  surface;  b,  buccal  surface;  d,  distal  surface;  0,  occlusal  surface; 
g,  gingival  line.  This  line  passes  entirely  around  the  tooth  at  the  junction  of  the 
crown  with  the  root. 

Diagram  B  (Patv-7).— The  Names  and  Positions  of  the  Line  Angles  of  a 
Mola?.  mb,  Mesio-buccal  angle;  ml,  mesio-lingual  angle;  db,  disto-buccal  angle;  dl, 
disto-lingual  angle;  mo,  mesio-occlusal  angle;  do,  disto-occlusal  angle;  bo,  bucco- 
occlusal  angle;  lo,  linguo-occlusal  angle.  The  names  of  the  occlusal  line  angles 
(the  last  four)  are  seldom  used,  as  they  are  called  also  marginal  ridges. 

Diagram  C  (Eax.-?). — The  Names  and  Positions  of  the  Point  Angles  of 
THE  Teeth.  It  will  be  noticed  that  these  angles  are  formed  by  the  junction  of  three 
surfaces  forming'  a  corner  or  point,  and  that  the  names  of  three  surfaces  form  the 
name  of  the  angle,  mbo,  mesio-buccal-occlusal  angle;  mlo,  mesio-linguo-occlusal 
angle;  dbo,  disto-bucco-occlusal  angle;  dio,  disto-linguo-occlusal  angle;  mbg,  mesio- 
bucco-gingival  angle;  mig,  mesio-linguo-gingival  angle;  dbg,  disto-bucco-gingivnl 
angle;  dig,  disto-linguo-gingival   angle. 


NOMENCLATURE.  1 1 


of  a  triangle.  They  are  named  after  the  cusps  to  which  they 
belong,  as  the  triangular  ridge  of  the  mesio-buccal  cusp  of  the 
upper  first  molar,  or  simply,  mesio-buccal  triangular  rid^. 
When  a  buccal  and  a  lingual  triangular  ridge  join  they  form  a 
transverse  ridge.  In  this  way  they  often  subdivide  the  cen- 
tral fossa  of  the  lower  molars  and  form  supplemental  fossae. 

10.  A  generally  rounded  or  angular  depression  on  the 
surface  of  a  tooth  is  called  a  fossa.  Fossae  occur  mostly  on  the 
occlusal  surfaces  of  the  molars.  When  a  notable  depression  is 
long-shaped  it  is  called  a  sulcus.  Some  of  these  pass  mesio- 
distally  entirely  through  the  occlusal  surface  of  a  tooth,  as  in 
the  bicuspids.  This  term  is  often  erroneously  applied  to  the 
grooves  and  fissures. 

11.  A  shallow,  long-shaped  depression,  in  the  form  of  a 
line,  on  the  surface  of  a  tooth,  is  called  a  groove.     When  such  / 
a  groove  follows  the  bottom  of  a  sulcus  it  is  said  to  be  sulcate.  j 
When  such  a  groove  sinks  suddenly  into  the  substance  of  a 
tooth  in  the  form  of  a  fault  it  is  called  a  fissure.    The  words 
sulcus,  groove,  and  fissure  are  often  used  as  if  they  were  syn- 
onymous and  interchangeable,  which  has  given  rise  to  much 
confusion.  It  is  necessary  that  the  distinctions  made  in  their  use 
in  dental  anatomy  be  well  understood.     A  groove  is  a  very  fine 
line  in  the  form  of  a  slight,  sharp  depression  on  the  surface  of 
the  tooth,  (as  represented  in  section  in  Diagram  D,  at  a  in  a 
section  cut  at  the  point  where  the  mesial  groove  passes  over  the 
marginal  ridge  of  a  bicuspid.    Diagram  E,  from  a  cross  section 
of  a  bicuspid,  very  close  to  the  occlusal  surface  grooves  are 
shown  at  a,  a.  j  A  very  shallow  depression  with  rounded  bot- 
tom is  also  called  a  groove,  as  those  seen  on  the  labial  surfaces 
of  the  incisors.    A  sulcate  groove  is  one  that  follows  a  sulcus  of 
notable  depth,  the  inclines  of  which  approach  each  other  at  an 
angle  'as  represented  in  Diagram  F,  a,  pointing  out  the  groove, 
and  c,  the  inclines  of  the  surface  of  the  tooth  which  form  the 
aulc-us.    A  fissure  is  always  a  fault  in  the  enamel,  a  point  where 
the  margins  of  the  plates  of  enamel  fail  to  unite,  as  represented 
at  a,  in  Diagram  G.    These  are  distinctions  of  importance,  and 


12 


NOMENCLATURE. 


there  should  be  no  confusion  in  the  use  of  the  words  by  which 
we  distinguish  them.  There  are  two  varieties  of  grooves  in  the 
teeth,  differing  essentially  in  their  nature  and  formation.  One 
class  mark  the  lines  on  which  the  parts  of  the  enamel  first 
formed  separately,  are  afterward  joined,  and  are  called  the  es- 
sential  or  developmental   grooves,  or   developmental   lines. 


D 


In  their  relation  to  the  development  of  the  enamel,  they  are  of 
the  same  nature  and  resemble  the  sutures  of  the  bones  of  the 
skull,  which  mark  the  junction  of  the  separately  formed  plates. 
The  parts,  or  divisions,  of  a  tooth  outlined  by  its  developmental 
grooves  are  called  its  lobes.  Most  human  teeth  have  four 
lobes ;  but  some  have  five  and  some  only  three.     Hence,  these 


NOMENCLATURE.  I3 


grooves  form  the  key  to  much  of  descriptive  dental  anatomy ; 
and  when  they  can  be  traced,  enable  the  anatomist  to  unravel 
complex  forms,  and  assign  irregularly-formed  teeth  to  the 
groups  to  which  they  belong,  to  properly  name  their  individual 
parts,  and  identify  any  additional,  accidental,  or  unusual  forms 
of  parts  that  may  have  become  intermingled  in  the  accident  of  a 
faulty  formation.  These  developmental  grooves,  or  lines,  are 
subject  to  fissures,  which  occur  when,  from  any  cause,  there  is 
a  failure  of  perfect  union  of  the  parts,  leaving  a  fault. 

12.  The  other  class  of  grooves  have  no  especial  relation 
to  the  developmental  lines,  and  are  called  supplemental 
grooves.  These  are  aptly  described  as  wrinkles  in  the  enamel, 
which,  in  fact,  many  of  them  are.  But  some  are  so  constant  in 
their  location  and'  form  as  to  make  up  a  portion  of  the  typical 
tooth-form.  The  supplemental  grooves  are  usually  shallow,  with 
well-rounded  bottoms,  and  are  not  ordinarily  subject  to  fissure. 

13.  In  the  mesio-distal  direction  all  of  the  teeth  are  a 
little  broader  at  or  near  their  occlusal  surfaces  than  at  their 
necks;  therefore,  as  they  stand  in  the  well- formed  arch,  their 
proximate  surfaces  touch  only  at  or  near  the  occlusal  margins 
of  their  proximate  surfaces,  leaving  V-shaped  openings  be- 
tween their  necks.  These  are  called  inter-proximate  spaces. 
Normally,  the  inter-proximate  spaces  are  filled  with  gum  tissue. 

__  In  the  bucco-lingual  direction  the  proximate  surfaces 
of  the  teeth  are  also  more  or  less  rounded,  so  that  the  proximate 
contact  is  narrowed  to  a  point  leaving  a  space  widening  toward 
the  buccal  and  a  space  widening  toward  the  lingual.  These  are 
called  the  buccal  and  lingual   inter-proximate    embrasures. 

14.  The  teeth  of  different  individuals  show  considerable 
variety  of  form.  Some  persons  have  teeth  with  very  long 
crowns,  broad  in  the  mesio-distal  direction  at  their  occlusal  sur- 
faces and  narrow  at  their  necks.  These  present  large  inter- 
proximate  spaces.  They  are  known  as  bell-crowned  teeth. 
Again,  some  individuals  have  teeth  that,  in  their  mesio-distal 
diameter,  are  nearlv  as  thick  at  their  necks  as  at  the  occlusal 


14  MEASUREMENTS   OF   THE  TEETH. 

surfaces,  making  their  inter-proximate  spaces  very  narrow,  the 
teeth  almost,  or  quite,  touching  along  the  whole  length  of  the 
crown.  These  are  known  as  thick-necked  teeth.  The  more 
common  form  is  midway  between  these  two  extremes.  The 
teeth  of  some  individuals  and  families  have  very  long  cusps ; 
those  of  others  have  very  short  cusps.  Some  are  deeply  marked 
by  grooves  and  sulci,  and  in  those  of  others  the  grooves  and 
sulci  are  shallow.  Thus,  there  is  considerable  variety  of  con- 
tour without  change  of  type. 

MEASUREMENTS  OF  THE  TEETH. 

15.  In  the  following  tables  the  results  of  the  measure- 
ment of  many  teeth  of  each  denomination  are  given.  The  num- 
bers measured  of  the  different  varieties  differed,  but  in  all  de- 
nominations they  were  sufficient  to  insure  reasonable  accuracy 
as  to  the  average  size.  There  are  three  measurements  given, 
the  average,  greatest,  and  least,  in  the  several  positions  meas- 
ured. With  a  greater  number,  both  larger  and  smaller  teeth 
might  be  found,  so  that  the  tables  must  not  be  taken  to  represent 
the  greatest  nor  the  least  that  might  be  obtained ;  but  the  occur- 
rence of  larger,  or  longer  teeth  must  be  rare. 

The  lines  of  measurement  are : 

ist.  "Length  over  all:"  Length  of  the  tooth  from  the 
cutting  edge,  or  buccal  cusp,  to  the  apex  of  the  root. 

2d.  "Length  of  crown :"  Length  of  the  crown  from  the 
cutting  edge,  or  buccal  cusp,  to  the  gingival  line  on  the  labial 
or  buccal  surface. 

3d.  "Length  of  root :"  Length  of  root  from  the  gingival 
line  on  the  buccal  surface  to  the  apex  of  the  root. 

4th.  "Mesio-distal  diameter  of  crown:"  This  is  the  ex- 
tent from  mesial  to  distal  in  the  greatest  diameter,  or  at  the 
points  of  proximate  contact. 

5th.  "Mesio-distal  diameter  of  neck:"  This  measurement 
was  made  at  the  gingival  line. 


'"  MEASUREMENTS    OF   THE   TEETH.  I5 

6th.  "Labio-  or  bucco-lingual  diameter:"  This  measure- 
ment was  taken  at  the  greatest  diameter  of  the  crown  in  the 
direction  named.  In  the  incisors  it  was  on  the  gingival  ridge. 
In  the  bicuspids  and  molars  it  was  generally  mid-length  of  the 
crown,  but  occasionally  it  was  near  the  gingival  line,  especially 
in  the  upper  second  and  third  molars. 

7th.  "Curvature  of  the  gingival  line :"  This  is  the  height 
or  extent  of  the  curve  of  the  gingival  line  toward  the  cutting 
edge,  or  occlusal  surface,  as  it  passes  from  labial  to  lingual, 
measured  on  the  mesial  surface. 

Having  these  tables,  the  necessity  for  giving  many  meas- 
urements in  the  text  is  avoided. 


i6 


MEASUREMENTS    OF    THE  TEETH. 


UPPER  TEETH. 


Tablk  of  Measurements  of  the 
Teeth    of    Man,  Given  in    Mil- 
limeters AND  Tenths  of  Milli- 
meters.* 

"3 

u 
<u 

c 

V 

0 

w 
0 

0 

"So 

c 

V 

0 

0 

u 

"0 

V 

«  2 

••So 
.2  S 

V     V 

"5 

0 
3  c 
1  0 
.2  S 

•5 

Si 

0  -a 

.2  1 
•2  " 

11 

1—    C 

0  -^ 
a  — 

3   _> 

>    C 

UPPER  TEETH. 

0 

^          1                    Average. 
Central                    Greatest. 
I^"^"-^-           Least. 

22.5 
27.0 
18.0 

lO.O 

12.0 

8.0 

12.0 

16.0 

8.0 

9.0 

lO.O 

8.0 

6.3 

7.0 

5-5 

7.0 
8.0 
7.0 

3.0 
4.0 

2.0 

Lateral                    GveltSt. 
I'^^'^^'^-            Least. 

22.0 
26.0 
17.0 

8.8 

10.5 

8.0 

13.0 

16.0 

8.0 

6.4 
7.0 

5-0 

4.4 
4.0 

6.0 
7.0 
5-0 

2.8 

4.0 
2.0 

Average. 
Cuspid.                    Greatest. 
Least. 

26.S 
32.0 
20.0 

9-5 

12.0 

8.0 

17-3 
20.5 

II.O 

7.6 
9.0 
7.0 

5-2 

6.0 
4.0 

8.0 
9.0 
7.0 

2.5 

3-5 

I.O 

T-.    ,                        Average. 
Fi«t                        Greatest. 
Bicuspid.         Least. 

20.6 
22.5 
17.0 

8.2 
9.0 
7.0 

12.4 
14.0 

lO.O 

7.2 
8.0 
7.0 

4-9 
6.0 
4.0 

9-1 

lO.O 

8.0 

I.I 
2.0 
0.0 

S"°°^                    GrelSt 
Bicuspid.         Least. 

21.5 
27.0 
16.0 

7-5 
9.0 
7.0 

14.0 
19.0 

lO.O 

6.8 
8.0 
6.0 

10.7 

12.0 

9.0 

5-3 
6.5 

4-5 

8.8 

lO.O 

7-5 

0.8 

1-5 
0.0 

Gr^e?: 
M^l^'^-            Least. 

20.8 
24.0 
17.0 

7-7 
9.0 
7.0 

13.2 

16.0 
10. 0 

7-5 
8.0 
7.0 

II. 8 
12.0 

II.O 

2.2 
3-0 
1.0 

S«°°d  ,                 Gr7at?st 
M°^"-            Least. 

20.0 
24.0 

i6.o 

7.2 
8.0 
6.0 

13.0 

17.0 

9.0 

9.2 

lO.O 

7.0 

6.7 
8.0 
6.0 

11.5 
12.5 

lO.O 

1.6 
4.0 
0.0 

„,  .   ,                      Average. 
^^''i,  ,                  Greatest. 
^°^^^-             Least. 

17.1 
22.0 
14.0 

6.3 
8.0 

5-0 

II. 4 
15.0 
8.0 

8.6 

II.O 

7.0 

6.1 
8.0 
5-0 

10.6 

14.5 
8.0 

0.7 

2.5 
0.0 

■  There  are  25.4  millimeters  to  the  inch. 


MEASUREMENTS    OF   THE   TEETH. 


17 


LOWER    TEETH. 


Table  of  Measurements  of  the 
Teeth   of   Man,   Given    in  Mil- 
limeters AND  Tenths  of  Milli- 
meters. 

0 
u 
0 

J3 
B 

0 
0 

u 
0 

M 

B 
V 

tn    0 

^    0 

"3 

0  1) 

CJ      4-1 

U     1> 

3     S 

0  ■« 

V 

•S   oJ 
(_    B 
0  S 
lU    » 

s  .> 

as  '5) 

0  °" 

LOWER    TEETH. 

C^°\'^k                       cleaSst 
I'^"^^^-              Least. 

20.7 
24.0 
16.0 

8.8 

10.5 

7.0 

II.8 

16.0 

9.0 

5-4 
6.0 
5.0 

3-5 
5.0 

2.5 

6.0 

6.5 

5-5 

2.5 
3-0 
1-5 

1  ateral                        Average. 
Lateral.                      Greatest. 

1°"^°^-              Least. 

21. 1 

27.0 
18.0 

9.6 

12.0 

7.0 

12.7 
17.0 
II. 0 

5-9 
6.5 
5° 

3.8 
3-0 

6.4 

7-5 
6.0 

2.5 
3-5 
2.0 

Average. 
Cuspid.                      Greatest. 
Least. 

25.6 

32.5 
20.0 

10.3 

12.0 

8.0 

15-3 
21.0 
II. 0 

6.9 
9.0 
5.0 

5-2 

7.0 
3-0 

7-9 

10. 0 

6.0 

2.9 
4.0 
2.0 

F"^^^.  ■       . ,            Grelte^t' 
Bicuspid.           Least. 

21.6 

26.0 
18.0 

7.8 
9.0 
6.5 

14.0 
18.0 
II. 0 

6.9 
8.0 
6.0 

4.7 
4.5 

7-7 
8.0 
7.0 

0.8 
1-5 
0.5 

0         J                       Average. 
S«^°?^«i        .,           Greatest. 
Bicuspid.           Least. 

22.3 

26.0 
18.0 

7-9 

lo.o 

6.0 

14.4 
17-5 
II-5 

7-1 

8.0 
6.5 

4.8 

6.5 
4.0 

8.0 
9.0 
7.0 

0.6 
2.0 
0.0 

_.    ^                           Average. 
^''%  ,                    Greatest. 
^°^^'-               Least. 

21.0 

24.0 

18.0 

7-7 

10. 0 

7.0 

13.2 
15.0 
II. 0 

II. 2 

12.0 
II. 0 

8.5 
9-5 
7-5 

10.3 
"•5 

lO.O 

I.I 

2.0 
0.0 

c,          ,                       Average. 
S^'^^^f  ,                     Greatest. 
^^°^^'-               Least. 

19.8 
22.0 
18.0 

6.9 
8.0 
6.0 

12.9 
14.0 
12.0 

10.7 
II. 0 

lO.O 

8.1 

8.5 
8.0 

10. 1 

10.5 

9-5 

0.2 

I.O 

0.0 

^rist. 
^°1"-                Least. 

18.5 

20.0 
16.0 

6.7 
8.0 
6.0 

11.8 

17.0 

8.0 

10.7 

12.0 

8.0 

8.3 
9.5 

5.0 

9.8 

10.5 

9.0 

0.2 

1-5 
0.0 

MEASUREMENTS    OF    THE   TEETH. 


UPPER  AND  LOWER  TEETH. 


Table  of  Measurements  of  the 
Deciduous      Teeth       of      Man, 
Given      in      Millimeters      and 
Tenths   of    Millimeters. 

> 
0 

Si 

bi 

n 

0 

u 
0 

0 
M 

c 

D 
►J 

0 
£ 

V 

0 

"^    ^ 

TO     tj 

to   -^ 

^     ° 

6  S 

|| 

-5 

1 S 
^  "0 
i  s 

S  2 

.5  0 
0  4; 

«  s 

►J    rt 

■5 

.—    0 
01    v 
a   c 
btu. 

.B  0 

T     u 

0     (U 

IS  ■£ 

Averages  Only. 

•5 

UPPER  TEETH. 

Central  Incisor. 

16.0 

6.0 

10. 0 

6.5 

4-5 

5-0 

4.0 

Lateral  Incisor. 

15.8 

5-6 

II.4 

51 

3-7 

4.8 

3-7 

Cuspid. 

19.0 

6.5 

13-5 

7.0 

5-1 

7.0 

5-5 

First  Molar. 

15-2 

5.1 

10.0 

7-3 

5-2 

8.5 

6.9 

Second  Molar. 

17-5 

5-7 

II. 7 

8.2 

6.4 

lO.O 

8.3 

LOWER  TEETH. 

Central  Incisor. 

14.0 

S.o 

9.0 

4.2 

3-0 

4.0 

3-5 

Lateral  Incisor.                                    15.0 

5-2 

lO.O 

4.1 

3-0 

4.0 

3-5 

Cuspid.                                                     17.0 

6.0 

1 

"•5 

50 

3-7 

4.8 

4.0 

First  Molar. 

15.8 

6.0 

9.8 

7-7 

6.5 

7.0 

5-3 

Second  Molar. 

18.8 

5-5 

11.3     9.9 

7-2 

8.7 

6.4 

MEASUREMENTS    OF    THE   TEETH. 


IQ 


UPPER   TEETH. 


Table  of    Measurements  of  the 
Teeth    of    Man,  in  Inches  and 
Hundredths  of  an  Inch. 

u 

V 

> 

O 

0 
0 
'0 

oi 

c 

V 

►J 

0 
0 

0 

J3 
M 

C 
D 

J 

■3  2 

V  0 
0  1-. 

CJ     1) 

S 
•5 

1  ^ 
1  0 

.2  ^ 
S  E 

■5 

si 

6  g 
■2  *« 

1*    . 

■"   a 
0  '•^ 
u  •-; 
3    > 

UPPER  TEETH. 

U 

Central.                  ^^S 
I""^^'--            Least. 

.88 
i.o6 

.72 

•39 
.41 
•31 

•49 
•63 
•31 

•35 
•39 
•31 

.24 

•27 
.21 

•27 
.31 
•27 

.11 

•15 
.07 

Lateral                     Greatlt. 
1°"^°'^-            Least. 

.86 

1.02 

.66 

•34 
.41 

•31 

•51 
•63 
■31 

•25 
•27 
.19 

•17 
■  19 
•15 

•23 
•23 
•19 

.11 

•15 

.07 

Average. 
Cuspid.                    Greatest. 
Least. 

1.04 

1.26 

•79 

•37 
•47 
•31 

.68 
.80 
•43 

.29 
■35 
•27 

.20 
•23 
•15 

•31 

•35 
•27 

.09 
•13 
•03 

T7-    ^                         Average. 

^''%.         .,          Greatest. 

Bicuspid.         Least. 

.81 
.89 
.66 

•32 
•35 

.27 

.48 
•55 
•39 

.28 

•31 

.27 

.19 
•23 

•15 

•35 
•39 
•31 

.04 
.07 
.00 

,,          ,                     Average. 
^«^°^^        .,          Greatest. 
Bicuspid.        Least. 

.84 

1.06 

.62 

•29 
.29 

•27 

.55 
•55 
•39 

.26 
•31 
•23 

.20 
•25 
.17 

•34 
•39 
•  29 

•03 
•05 
.00 

First                          Average. 

.81 

•94 
.66 

•30 
•35 
•27 

•51 

.62 

•39 

.42 
•47 
•35 

.29 
•31 
•27 

.46 
•47 
•43 

.08 
.11 
•03 

Second                    ^^^-^fSt 
Molar.              f'-^^^^t- 
Least. 

.78 

•94 
.62 

.28 
•31 
•23 

•51 
.66 

•35 

.36 
•39 

•27 

.26 
•31 
•23 

•45 
•49 
•39 

■05 
•15 

.00 

Third                       ^^^'"fgt 
Molar.              Greaest. 
Least. 

.67 
.86 

.55 

•24 
•31 
•19 

•44 
•59 
•31 

•33 

•43 
.27 

•23 
•31 
•19 

.41 
•57 
•31 

.02 
.09 
.00 

20 


MEASUREMENTS    OF   THE  TEETH. 


LOWER  TEETH. 


Table  of  Measurements   of  the 
Teeth  of  Man,  in    Inches    and 
Hundredths  of  an  Inch. 

u 

V 

o 

c 

4) 

0 

u 

"o 
"S) 

c 

4> 

0 

0 

5 

►J 

c 
5  2 

in    0 

n 

in    1) 

s 

•5 

—    u 
cd    V 

■5  0 

•2  i 

S  4! 

8  5 

3-5 

0 

■5  « 
0  — 

4>   ^^ 

u    rt 
3    > 

rt  'So 
>   c 

3   'So 

LOWER  TEETH. 

U 

^°"^°'^-            Least. 

.80 
.63 

•34 
.41 
.27 

•47 
.62 

•35 

.22 
.23 
•19 

•13 
.19 
.09 

•23 
.26 

.21 

.09 
.11 

•05 

L^t^^l  .                  GreatTt! 
1°"^°^-            Least. 

.83 

1.06 

.70 

•35 
.46 
.27 

.50 
.66 
•43 

•23 
.26 

•  19 

•15 
.19 
.11 

•25 
•29 
•25 

.09 

•13 

.08 

Average. 
Cuspid.                     Greatest. 
Least. 

1. 01 
1.28 

.78 

.40 
.46 
•32 

.60 
.82 
•43 

.27 
•35 
•23 

.20 

■27 
.11 

•31 

•39 

.24 

.11 
.14 

.08 

First                         Average. 

Bicuspid.  £:r'- 

.84 
1.02 

.30 
•  35 
•25 

•  54 
.70 

.43 

.27 
•32 
•23 

.18 
.20 
.16 

•30 
•31 

.27 

•03 
•05 
.01 

Second                     Average. 
T>-         -J          Greatest. 
Bicuspid.         Least. 

.87 
1,02 

•7» 

•31 

•43 
•23 

.56 
•63 
•  45 

.28 
.32 
•25 

.18 
•25 
•15 

•31 

•35 

•27 

.02 
.07 
.00 

First                         ^^^"g^- 
Molar.              Greaest. 
Least. 

.78 
•94 
•71 

•30 
•39 
•27 

•52 
•59 
.43 

•33 
•37 
.23 

•33 
•37 
•29 

.40 
•45 
•39 

.04 
.07 
.00 

Second                     i^^"f^^- 
Molar.              ^-■ 

.78 
.86 
•71 

•27 
•31 
•23 

•50 
•55 
•47 

•42 
•43 
•39 

•32 
.33 
•31 

•39 
.41 
•37 

.00 
.00 
.00 

Third                       Average. 
.r   ,                  Greatest. 
Molar.              T 

Least. 

•72 
.78 

•63 

.26 
•32 
■23 

•36 
.66 

•31 

•42 
•47 
•31 

•32 
•37 
.20 

•38 

.41 

•35 

.00 
.04 
.00 

MEASUREMENTS    OF    THE   TEETH. 


21 


UPPER  AND  LOWER  TEETH. 


Table  of  Measurements  of  the 
Deciduous  Teeth  of  Man,  Given 
IN  Inches  and  Hundredths  of  an 
Inch. 

> 
o 
.a 

M 
V 

J 

0 
u 

0 
.a 
"m 

V 

J 

1 
0 . 

c 

i 

« g 

^      0 

0     u 
'm    ^^ 

■5 

2.  % 
-■B  0 
.2  fe 

.2 
•5 

.E  ° 

0  s 

•5 

-lingual 
r  of  neck. 

Averases  Only- 

UPPER  TEETH. 

Central  Incisor. 

•63 

1 

•23     .39  1  -25     -18 

.20 

.16 

Lateral  Incisor. 

.62 

•25 

•45    ;  -20  ^  .14 

•19 

.14 

Cuspid. 

•74 

•25 

•53     -27  1  -20 

•27 

.21 

First  Molar. 

•59 

.20 

•39 

.28 

.20     .33 

•27 

Second  Molar. 

.68 

.22 

•46 

.32 

•25     -39 

•32 

LOWER  TEETH. 

Central  Incisor. 

•55 

•19 

1 

•  35  1  -15 

1 

.11 

•15 

•13 

Lateral  Incisor. 

•59 

.19    .39    -IS 

1         1 

•"  j  -15 

1 

■13 

Cuspid. 

.66 

•23      45 

i 

•19 

.14 

•17 

•15 

First  Molar. 

.62 

24     .38 

•30 

•25 

.27 

.21 

Second  Molar. 

.62 

.21     .44    .38 

i         i 

.28 

•34 

•25 

UPPER    CENTRAL    INCISORS. 


UPPER  CENTRAL  INCISORS. 

Note. — Usually,  in  the  descriptions  of  the  teeth,  those  of  one  side 
only  will  be  mentioned,  without  reference  to  which  side  in  the  text. 
Accompanying  the  illustrations,  the  side  to  which  the  tooth  belongs 
will  be  given.  The  student  will  readily  determine  to  which  side  a 
given  example  belongs  by  comparing  it  with  the  text  and  correctly 
naming  its  surfaces.  Students  should  remember  that  the  cuts  are 
representations  of  individual  teeth,  while  the  text  describes  the  aver- 
age forms,  therefore  the  cuts  will  not  always  exactly  correspond  with 
the  text. 

1 6.  The  right  and  left  upper  central  incisors  are  situated 
in  the  extreme  anterior  part  of  the  dental  arch,  one  on  each 
side  of  the  median  line,  their  mesial  surfaces  proximating  each 
other.  The  cro"wn  presents  four  surfaces,  four  angles,  and  a 
cutting  edge,  or  incisal  surface.  The  general  contour  of  the 
crown  is  similar  to  a  wedge,  with  rounded  angles,  and  merging 
into  a  rounded  form  at  the  thick  end,  or  the  neck  of  the  tooth. 
It  is  slightly  bent  on  its  shorter  diameter,  so  as  to  make  the 
flattened  labial  surface  convex;  while  the  other,  the  lingual,  is 
concave.  The  crown  is  also  slightly  bent  in  the  mesio-distai 
direction,  so  that  the  labial  surface  is  convex  and  the  lingual 
concave  in  this  direction.  Therefore,  there  is  a  general  con- 
vexity of  the  labial",  and  a  general  concavity  of  the  lingual  sur- 
face. 

17.  The  labial  surface  of  the  crown  of  the  upper  central 
incisor  (Fig.  i),  in  its  general  form,  is  an  imperfect  square, 
with  its  gingival  side  rounded.  The  mesial  margin  is  a  little 
longer  than  the  distal,  so  that  the  cutting  edge  slopes  away 
toward  the  disto-incisal  angle  (Fig.  i,  h).  Both  the  angles, 
formed  by  the  proximate  surfaces  and  cutting  edge,  are  slightly 
rounded,  the  disto-incisal  more  than  the  mesio-incisal,  after 
which  the  proximate  surfaces  converge  toward  the  long  axis  of 
the  tooth,  making  the  crown  a  little  narrower  at  the  neck  than 
at  the  cutting  edge. 

18.  The  lingual  surface  of  the  crown  (Fig.  2)  is  con- 
cave in  all  directions,  forming  a  fossa,  bounded  by  the  cutting 
edge  (a),  the  mesial  and  distal  marginal  ridges  (n,  m),  and  the 


Fie.  4. 


Fig.  5. 


Fig.  I*  (Par.  17). — Right  Upper  Central  Incisor,  Labial  Surface,  a,  Cut- 
ting edge;  b,  mesial  surface;  c,  distal  surface;  d,  labial  surface;  e,  e,  labial  grooves; 
g,  mesio-incisal  angle;  /;,  disto-incisal  angle;  i,  body  of  root;  k,  apex  of  root. 

Fig.  2*  (Par.  18). — Right  Upper  Central  Incisor,  Lingual  Surface,  a.  Cut- 
ting edge;  b,  mesial  surface;  c,  distal  surface;  d,  linguo-gingival  ridge,  or  cingu- 
lum;  /,  gingival  line;  g,  mesio-incisal  angle;  /;,  disto-incisal  angle;  i,  body  of  root; 
k,  apex  of  root;  m,  distal  marginal  ridge;  n,  mesial  marginal  ridge. 

Fig.  3*  (Par.  18). — Left  Upper  Central  Incisor,  Lingual  Surface,  showing 
lingual  pit.  The  cutting  edge,  a,  is  considerably  worn.  The  mesial  and  distal  mar- 
ginal ridges,  b,  c,  are  prominent;  d,  linguo-gingival  ridge;  f,  gingival  line;  ff, 
mesio-incisal  angle;  /;,  disto-incisal  angle;  j,  body  of  root;  k,  apex  of  root;  m, 
lingual  pit. 

Fig.  4*  (Par.  19). — Right  Upper  Central  Incisor,  Mesial  Surface,  a.  Mesio- 
incisal  angle;  d,  linguo-gingival  ridge;  f,  f,  gingival  line,  showing  its  labio-lingual 
curvature;   i,   body  of  root;   k,  apex  of  root. 

Fig.  s*  (Par.  21). — Left  Upper  Central  Incisor,  Lingual  Surface.  Young, 
unworn  tooth.  The  developmental  lines,  or  grooves,  are  made  diagrammatically 
prominent  to  show  the  form  of  the  lobes,  a,  Middle  lobe;  b,  mesial  lobe;  c,  distal 
lobe;  d,  lingual  lobe;  e,  e,  linguo-gingival  groove;  /,  f,  lingual  developmental 
grooves;  g,  mesio-incisal  angle;  h,  disto-incisal  angle. 


'Illustration,   lyi  diameters. 


UPPER    CENTRAL    INCISORS. 


linguo-gingival  ridge,  or  cingulum  (d).  The  marginal  ridges 
are  strong  elevations  of  the  enamel,  running  from  the  mesio- 
incisal  and  disto-incisal  angles  along  the  borders  of  this  sur- 
face to  near  the  gingival  line,  where  they  join  the  linguo-gingi- 
val ridge.  The  linguo-gingival  ridge  is  a  strong  elevation  of 
the  enamel  forming  the  linguo-gingival  border  of  the  crown. 
It  is  sometimes  elevated  into  a  tubercle.  The  lingual  fossa  is 
usually  smooth,  and  the  ridges  by  which  it  is  bounded  are  not 
prominent.  In  many  instances,  however,  there  is  a  deep  pit  at 
the  junction  of  the  linguo-gingival  ridge  with  the  lingual  sur- 
face proper;  and  in  some  a  groove  extends  from  the  pit  for  a 
short  distance  along  the  border  of  each  marginal  ridge  (Fig. 
3).  These  latter  may,  or  may  not,  be  fissured.  In  a  few  ex- 
amples the  enamel  of  this  surface  has  irregular  wrinkles,  or 
ridges  and  grooves,  running  from  the  linguo-gingival  ridge 
toward  the  cutting  edge.  In  malformed  teeth  this  surface  is 
often  very  imperfect. 

19.  The  mesial  and  distal  surfaces  each  present  the 
outline  of  the  letter  V,  with  its  lines  curved  with  the  convexity 
toward  the  lips,  and  the  acute  angle  at  the  cutting  edge  (Fig. 
4).  The  mesial  surface  is  almost  straight  from  the  mesio- 
incisal  angle  to  the  gingival  line.  It  Is  convex  from  labial  to 
lingual,  but  nearly  flat  toward  the  gingival  line ;  while  in  some 
there  is  even  a  slight  concavity,  centrally  at,  or  near,  the  gingi- 
val line.  In  the  labio-lingual  direction,  the  distal  surface  is 
rounded,  as  in  the  mesial.  In  the  majority  of  examples  it  is 
also  convex  in  the  direction  of  the  long  axis  of  the  tooth,  so 
that  it  bellies  out  toward  the  lateral  incisor. 

20.  At  the  gingival  line,  the  tooth  is  a  little  constricted, 
forming  a  slight  furrow ;  or  rather,  the  root  at  the  neck  is  a 
little  smaller  than  the  crown,  and  the  enamel  slopes  down  to 
the  size  of  the  root,  giving  the  appearance  of  a  continuous  ridge 
of  enamel  around  the  neck.  This  line  does  not  run  horizon- 
tally around  the  neck  of  the  tooth.  On  the  proximate  sides 
it  forms  curves  with  the  convexity  toward  the  crown,  that  on 
the  mesial  being  a  little  the  greater,  and  on  the  labial  and  lin- 


26  UPPER    CENTRAL    INCISORS. 

gual  surfaces  it  forms  a  curve  with  the  concavity  toward  the 
crown.  This  line  marks  the  limit  of  the  attachment  of  the  peri- 
dental membrane  and  gum  tissue  to  the  root  of  the  tooth. 

21.  Developmental  lines  (Fig.  5).  When  any  of  the 
incisors  first  appear  through  the  gums  there  are  three  little  emi- 
nences, or  tubercles,  called  mammelons,  on  the  cutting  edge 
with  grooves  crossing  from  labial  to  lingual  between  them 
(a,  g,  h).  These  grooves  run  some  distance  on  the  labial  sur- 
face, becoming  broader  and  shallower  till  they  disappear.  In 
many,  these  lines  appear  on  the  lingual  surface  between  the 
marginal  ridges  and  the  fossa  (f,  f).  Occasionally,  they  are 
seen  as  far  as  the  linguo-gingival  ridge.  The  mammelons  are 
soon  removed  from  the  edge  by  wear,  leaving  it  straight,  or 
slightly  curved.  These  lines  divide  this  part  of  the  crown  of 
the  tooth  into  three  labial  lobes.  Calcification  begins  in  these 
mammelons  as  separate  pieces,  or  plates,  and  the  grooves  are 
the  marks  of  the  after-confluence  of  these  plates.  This  is  com- 
mon to  the  incisors  and  cuspids.  These  teeth  are  sometimes 
fissured  across  the  cutting  edge,  marking  an  imperfect  conflu- 
ence of  the  primary  plates.  The  calcification  of  the  linguo-gin- 
gival ridge,  or  cingulum,  is  also  begun  as  a  separate  plate,  form- 
ing the  lingual  lobe,  but  afterward  it  becomes  united  to  the 
other  parts  by  confluence,  leaving  a  groove,  often  very  slight, 
indeed,  and  soon  obliterated  by  wear,  marking  the  line  of 
union.  This  is  the  linguo-gingival  groove  (e,  £?),  (This 
groove  is  properly  three  grooves  corresponding  with  the  mesial, 
central,  and  distal  grooves  of  the  bicuspids,  while  the  linguo- 
gingival  ridge  corresponds  to  the  lingual  cusp.  See  Par.  41.) 
In  smooth  regularly  formed  teeth  it  begins  at  the  gingival  line 
just  lingual  of  the  summit  of  its  labio-lingual  curvature,  and 
runs  across  the  marginal  ridge  at  right  angles  with  its  length, 
then  runs  almost  horizontally  across  the  lingual  surface  to  the 
distal  marginal  ridge.  This  ridge  is  now  crossed  at  right  angles, 
and  the  gingival  line  reached.  The  length  of  the  groove  usually 
includes  from  a  quarter  to  a  third  of  the  circumference  of  the 
tooth.     When  the  linguo-gingival  ridge  is  prominent,  or  rises 


r-A 


Fig.  6*  (Par.  24).— Right  Upper  Lateral  Incisor,  Labial  Surface,  o,  Cut- 
ting edge;  c,  distal  surface;  c,  labial  grooves;  /,  gingival  line;  g,  mesio-incisal 
angle;  /;,  disto-incisal  angle. 

Fig.  7*  (Par.  25). — Right  Upper  Lateral  Incisor,  Mesial  Surface,  a, 
Mesio-incisal  angle;  d,  linguo-gingival  ridge;  /,  f,  gingival  line;  t,  body  of  root;  k, 
apex   of  root. 

Fig.  8*  (Par.  26). — Right  Upper  Lateral  Incisor,  Lingual  Surface,  without 
lingual  pit;  a,  Cutting  edge;  b,  mesial  marginal  ridge;  c,  distal  marginal  ridge;  d, 
linguo-gingival  ridge;  f,  gingival  line;  g-,  mesio-incisal  angle;  k,  disto-incisal  angle; 
>',  body  of  root;  k,  apex  of  root;  m,  lingual  fossa. 

Fig.  9*  (Par.  26). — Right  Upper  Lateral  Incisor,  Lingual  Surface,  with 
lingual  pit.  a,  Cutting  edge;  b,  mesial  marginal  ridge;  c,  distal  marginal  ridge, 
with  linguo-gingival  groove  crossing  it;  d,  linguo-gingival  ridge,  or  cingulum;  /, 
gingival  line;  g,  mesio-incisal  angle;  /;,  disto-incisal  angle;  1,  body  of  root;  k,  apex 
of  root;  tn,  lingual  pit. 

Fig.  10*  (Par.  26). — Right  Upper  Lateral  Incisor,  showing  a  linguo-gingival 
fissure,  a.  Cutting  edge;  b,  linguo-gingival  groove  fissured;  /j  gingival  line;  g, 
mesio-incisal  angle;  h,  disto-incisal  angle. 

Fig.  II*  (Par.  27). — Upper  Lateral  Incisor,  Mesial  Surface.  Very  short 
root,     a,  mesio-incisal  angle;  d,  linguo-gingival  ridge;   f,  gingival  line. 


'Illustration,   ij^   diameters. 


UPPER  LATERAL   INCISOR.  29 

in  the  form  of  a  tubercle,  this  groove  is  subject  to  much  varia- 
tion in  its  course.  Often,  there  is  a  deep  pit  in  the  center  of  its 
length;  i.e.,  centrally  in  the  lingual  surface,  at  the  margin  of 
the  linguo-gingival  ridge  (Fig.  3,  m).  From  this,  fissures 
may  extend  laterally.  Occasionally,  especially  in  the  lateral 
incisors,  a  sulcus,  or  a  fissure  divides  the  linguo-gingival  ridge 
from  one  of  the  marginal  ridges,  and  extends  into  the  cemen- 
tum  (Fig.  10).    This  is  the  linguo-gingival  fissure. 

22.  The  root  of  the  upper  central  incisor  (Figs,  i  to  5) 
is  about  one  and  a  fourth,  to  one  and  a  half  times  as  long  as 
the  crown.  It  is  conical  in  form,  tapering  from  the  crown  to 
the  apex;  less  rapidly  near  the  neck,  and  more  rapidly  as  the 
apex  is  approached.  Therefore,  the  body  of  the  root  seems  a 
little  swollen.  However,  the  root  of  this  tooth  presents  great 
variety  of  figure,  as  do  the  roots  of  teeth  generally.  The  root 
is  nearly  round  at  the  neck.  The  curvature  of  the  lingual  sur- 
face is  the  arc  of  a  smaller  circle  than  that  of  the  labial.  The 
proximate  surfaces  are  slightly  flattened.  The  flattened  por- 
tion of  the  mesial  surface  is  a  little  broader  than  the  distal. 
These  two  converge  to  the  lingual,  giving  the  form  of  a  prism 
with  its  angles  rounded. 

UPPER  LATERAL  INCISOR. 

23.  The  description  of  the  lateral  incisor  may  be  much 
abridged,  because  of  its  resemblance  to  the  central  in  its  gen- 
eral form  and  developmental  lines.  The  tooth  is  a  little 
shorter,  and  from  mesial  to  distal  the  crown  is  about  a  third 
narrower. 

24.  The  labial  surface  of  the  lateral  incisor  (Fig.  6)  is 
more  rounded  in  the  mesio-distal  direction  than  in  the  central. 
The  mesio-incisal  angle  is  acute,  and  the  cutting  edge  slopes 
away  in  a  curve  to  a  rounded  and  obtuse  disto-incisal  angle. 
The  cutting  edge,  at  the  time  of  eruption,  presents  three  tuber- 
cles, or  mammelons,  and  the  grooves  crossing  the  edge  between 
these  are  projected  on  the  labial  surface  as  shallow  labial 
grooves. 


30  UPPER   LATERAL  INCISOR. 

25.  The  mesial  (Fig.  7)  and  distal  surfaces  present 
the  characteristic  V-shape  of  all  the  incisors.  From  labial  to 
lingual  the  mesial  surface  is  rounded  near  the  cutting  edge,  but 
much  flattened  near  the  gingival  line./  Sometimes  a  slight  con- 
cavity exists  at  this  point.  Occasionally  the  mesio-labial  angle 
has  a  flattened  or  sunken  point  of  enamel  near  the  middle  of  its 
length.  This  is  sometimes  broad  and  of  notable  depth,  and  in 
this  case  is  generally  in  the  labial  portion  of  the  mesial  surface. 
In  others,  it  is  a  small  imperfection  in  the  mesial  margin  of  the 
labiail  surface.  The  distal  surface  is  convex  in  all  directions. 
In  its  incisal  third,  it  rounds  out  freely  toward  the  cuspid,  but 
becomes  more  flattened  toward  the  gingival  line. 

26.  The  lingual  surface  (Fig.  8)  of  lateral  incisors  is 
very  irregular  in  the  extent  of  its  concavity.  Some  are  almost 
flat,  while  others  are  deeply  concave.  The  mesial  and  distal 
marginal  ridges  are  proportionately  broader  and  stronger  than 
in  the  centrals.  In  the  majority  of  examples  the  lingual  sur- 
face is  the  broadest  part  of  the  crown.  The  rounding  of  the 
proximate  surfaces  is  at  the  expense  of  the  labial  surface,  so 
that  a  moderately  acute  angle  is  formed  by  the  junction  of  the 

"proximate  surfaces  with  the  lingual.  '  Generally,  the  lingual 
surface  is  almost  smooth,  but  in  many,  a  pit,  with  or  without 
lateral  fissures,  will  be  found  at  the  junction  of  the  lingual  sur- 
face proper,  with  the  linguo-gingival  ridge  (Fig.  9).  In  some 
of  these,  the  linguo-gingival  ridge  is  unusually  short,  so  that 
the  marginal  ridges  are  folded  in  together  at  their  gingival 
ends,  forming  a  deep  sulcus  between  them,  and  there  is  a  deep 
pit  at  their  junction.  Again,  some  are  found  in  which  there  is 
a  deep  groove,  which  is  often  fissured  dividing  one  marginal 
ridge  from  the  linguo-gingival  ridge,  and  extending  into  the 
cementum  (Fig.  10).  This  is  sometimes  nearly  central,  giving 
the  appearance  of  a  failure  of  the  lingual  lobe,  or  of  a  division 
of  the  lobe  centrally,  or  of  the  displacement  of  the  lobe  to  one 
side.    This  is  the  linguo-gingival  fissure. 

27.  The  root  of  the  upper  lateral  incisor  (Figs.  6  to  11) 


,  Fig.  12. 


FiR-  15- 


Fig.  12*  (Par.  29). — Left  Lower  Central  Incisor,  Labial  Surface.  Long 
root,  a.  Cutting  edge;  e,  labial  grooves;  /,  gingival  line;  g,  mesio-incisal  angle;  h, 
disto-incisal  angle. 

Fig.  13*  (Par.  29). — Left  Lower  Lateral  Incisor,  Labial  Surface.  Long 
root,  a,  Cutting  edge;  e,  labial  grooves;  /,  gingival  line;  g,  mesio-incisal  angle;  h, 
disto-incisal   angle;  i,   body   of  root;   k,  apex   of  root. 

Fig.  14*  (Par.  29). — Right  Lower  Lateral  Incisor,  Labial  Surface.  Short 
root,  a.  Cutting  edge;  e,  labial  grooves;  /,  gingival  line;  g,  mesio-incisal  angle;  h, 
disto-incisal  angle;   i,  body  of  root;  k,   apex  of  root. 

Fig.  15*  (Par.  30). — Lower  Central  Incisor,  Lingual  Surface,  a,  Cutting 
edge;  /;.  mesial  marginal  ridge;  c,  distal  marginal  ridge;  d,  linguo-gingival  ridge;  g, 
mesio-incisal  angle;  h,  disto-incisal  angle;  m,  lingual  ridge. 

Fig.  16*  (Par.  30). — Lower  Central  Incisor,  Distal  Surface,  a.  Cutting 
edge;  the  edge  is  worn  away  as  represented  by  the  line;  d,  linguo-gingival  ridge; 
f,  f,   gingival  line;  i,  groove  along  the  distal  side  of  root;  k,  apex  of  root. 

Fig.  17*  (Par.  31). — Right  Lower  Lateral  Incisor,  Distal  Surface,  showing 
root  deeply  grooved,  a,  Cutting  edge;  d,  linguo-gingival  ridge;  f,  gingival  line;  t" 
deep  groove  in  root;   k,  apex  of  root. 


^Illustration,    ij^    diameters. 
4 


THE    LOWER    INCISORS.  33 

is  conical,  but  considerably  flattened  on  its  mesial  and  distal 
sides,  which  is  generally  maintained  to  the  apex.  The  root  is 
generally  straight,  and  about  one  and  a  half  times  as  long  as 
the  crown.  In  many  specimens  the  apex  is  curved  to  the  distal. 
Occasionally  the  root  is  very  crooked. 

28.  The  upper  lateral  incisor  presents  much  variety  of 
size  and  form.  It  is  not  uncommon  to  find  narrow  laterals  as- 
sociated with  broad  centrals.  The  lateral  upper  incisors  are 
more  often  wanting,  or  imperfectly  developed,  than  the  other 
anterior  teeth.  In  the  latter,  the  crown  of  the  tooth  is  fre- 
quently conical,  with  a  rounded,  or  even  a  moderately  sharp, 
point. 

THE   LOWER   INCISORS. 

29.  The  lower  incisors  have  outlines  similar  to  the 
upper  lateral,  but  are,  in  every  way,  more  slender.  Their  de- 
velopmental lines  are  the  same,  but  the  grooves  are  much  less 

-^marked,  and  generally  cannot  be  seen  except  in  unworn  teeth. 
The  cutting  edge  of  the  lower  central  (Fig.  12)  is  very  nearly 
at  right  angles  with  the  long  axis  of  the  tooth,  and  its  mesio- 
and  disto-incisal  angles  are  square  and  sharp.  From  mesial  to 
distal,  the  cutting  edge  is  the  widest  part  of  the  crown,  and 
from  it  the  proximate  surfaces  converge  equally  to  the  gingival 
line,  reducing  the  mesio-distal  diameter  about  a  third.  ';  The 
lower  lateral  differs  from  the  central  by  the  cutting  edge  slop- 
ing away  to  the  distal,  the  mesio-incisal  angle  being  acute,  and 
the  disto-incisal  angle  obtuse  and  rounded.  The  distal  surface 
is  also  convex  from  the  disto-incisal  angle  to  the  gingival  line, 
bellying  out  toward  the  cuspid. 

30.  The  lingual  surface  (Fig.  15)  of  the  lower  incisors 
is  concave  from  the  cutting  edge  to  the  linguo-gingival  ridge, 
over  which  there  is  a  convexity  (Fig.  16).  'Near  the  cutting 
edge  this  surface  is  generally  nearly  flat  in  the  mesio-distal 
direction,  but  is  sometimes  concave  or  slightly  convex;  it  be- 
comes convex  progressively  toward  the  linguo-gingival  ridge. 
In  many  there  is  a  slight  ridge  on  the  center  of  this  surface  with 
a  shallow  concavity  on  either  side,  which  marks  the  junction  of 


34  THE  CUSPIDS. 


the  lobes,  running  from  near  the  cutting-edge  to  the  linguo- 
gingival  ridge  (Fig.  15).  The  mesial' and  distal  surfaces 
are  convex  near  the  cutting  edges,  but  become  flattened,  and 
sometimes  slightl}^  concave,  toward  the  gingival  line. 

31.  The  roots  of  the  lower  incisors  are  slender  and  much 
flattened  in  their  mesio-distal  diameter,  and  not  unfrequently 
slightly  grooved  on  the  mesial  and  distal  sides.  While  the  flat- 
tening of  the  crown  of  the  lower  central  is  generally  at  right 
angles  with  the  flattening  of  its  root,  the  distal  portion  of  the 
crown  of  the  lower  lateral  is  directed  more  to  the  lingual,  so  as 
to  appear  slightly  twisted  on  its  root  in  most  examples.  The 
labial  surface  of  the  crown  and  root,  in  its  length,  forms  nearly 
the  arc  of  a  circle  (Fig.  17),  though  the  curve  of  the  surface 
of  the  crown  is  usually  a  little  greater  than  that  of  the  root 
(Fig.  16).  The  lingual  surface  of  the  root  is  almost  straight, 
but  in  the  apical  third  it  is  conv^ex,  sloping  away  to  form  the 
apex.  The  roots  of  these  teeth  are  generally  straight,  but  occa- 
sionally the  apex  is  curved  to  the  distal. 

THE    CUSPIDS. 

32.  We  have  four  cuspids,  one  on  each  side  in  the  upper, 
and  one  on  each  side  in  the  lower  jaw.  They  are  sometimes 
called  canine  teeth,  or  eyeteeth.  They  are  situated  at  the  an- 
gles of  the  mouth,  between  the  lateral  incisors  and  the  first  bi- 
cuspids. They  are  third  from  the  median  line,  and  are  large, 
and  strong  teeth  of  simple  form,  firmly  implanted  in  the  alve- 
olar process  by  a  long,  strong  root. 

THE  UPPER  CUSPIDS. 

33.  The  labial  surface  of  the  crown  of  the  upper  cuspid 
(Fig.  18)  is  a  little  narrower  in  the  mesio-distal  direction  than 
in  the  central  incisor,  with  nearly  equal  length  from  the  point 
of  the  cusp  to  the  gingival  line.  Instead  of  a  straight,  or  only 
slightly  curved  cutting  edge,  as  in  the  incisors,  the  central  por- 
tion of  the  crown  is  extended  nito  a  well-formed  point    (a), 


Fig.  21. 


Fig;.  22.  Fig.  23.  Fig.  24. 

Fig.  18*  (Par.  33). — Right  Upper  Cuspid,  Labial  Surface,  a,  Point  of  cusp; 
d,  labial  ridge;  e,  labial  grooves;  /,  gingival  line;  g,  mesio-incisal  angle;  h,  disto- 
incisal  angle;   ;,   body  of  root;  k,  apex  of  root. 

Fig.  19*  (Par.  34).— Right  Upper  Cuspid,  Lingual  Surface.  The  more  com- 
mon form.  a.  Point  of  cusp;  d,  linguo-gingival-ridge;  e,  c,  lingual  grooves;  f, 
gingival  line;  g,  mesio-incisal  angle;  /;,  disto-incisal  angle;  i,  body  of  root;  k,  apex 
of   root;   7!!,    lingual   ridge. 

Fig.  20*  (Par.  34). — Right  Upper  Cuspid,  Lingual  Surface  of  irregular  form. 

a.  Point  of  cusp;  d,  linguo-gingival  ridge;  e,  e,  lingual  grooves;  /,  gingival  line;  g, 
mesio-incisal  angle;  h,  disto-incisal  angle;  m,  prominent  lingual  ridge;  n,  two  small 
tubercles   on   linguo-gingival   ridge. 

Fig.  21*  (Par.  35).— Right  Upper  Cuspid,  Mesial  Surface,    a.  Point  of  cusp; 

b,  mesial  marginal  ridge;  c,  point  of  slight  concavity  of  mesial  surface;  d,  linguo- 
gingival  ridge;  e,  labial  groove;  f,  f,  gingival  line;  g,  mesio-incisal  angle;  1,  body 
of  root;  k,  apex  of  root. 

Fig.  2?*  (Par.  37). — Left  Upper   Cuspid,  with  a  very  long  and  crooked  root. 
Fig.  23*  (Par.  37). — Right    Upper   Cuspid,   with   a   peculiarly   crooked   root. 
Fig.  24*  (Par.  3j). — Left  Upper  Cuspid,  with  a  very  small  and  short  root. 

*Illustration,    i^    diameters. 


THE    UPPER   CUSPID.  37 


with  cutting  edges  sloping  away  to  the  mesio-incisal  and  disto- 
incisal  angles  (g^  h).  Of  these  cutting  edges,  the  distal  is  a 
little  the  longer,  and  from  the  disto-incisal  angle  to  the  gingival 
line,  the  distal  surface  is  a  little  shorter  than  the  mesial.  In 
unworn  teeth,  the  angle  formed  by  the  union  of  the  cutting  edges 
to  form  the  cusp  is  usually  about  ninety  degrees,  or  a  square. 
The  point  is  a  little  rounded  at  first,  but  is  soon  much  rounded 
or  flattened  by  wear."  Both  the  mesial  and  distal  margins  of  the 
labial  surface  of  the  crown,  from  the  mesio-  and  disto-incisal 
angles  to  the  gingival  line,  slope  toward  the  central  axis  of  the 
tooth — the  distal  slope  being  the  greater.  This  narrows  the 
crown  at  the  neck  nearly  one-third  from  the  width  of  its  widest 
point.  The  curvature  of  the  gingival  line  on  this  surface, 
marking  the  termination  of  the  crown,  is  about  a  quarter  circle. 

-^T'he  surface  is  convex  in  all  directions,  and  is  much  more 
rounded  in  the  mesio-distal  direction  than  in  the  incisors.  In 
the  direction  of  its  length,  the  convexity  is  about  the  same  as  in 
the  incisors.  The  greater  convexity  mesio-distally  is  caused  by 
a  strong  labial  ridge  {d)  running  from  the  point  of  the  cusp 
to  the  gingival  line.  This  ridge  occupies  so  much  of  the  sur- 
face of  the  tooth  that  its  margins  are  imperfectly  defined.  It 
belongs  to  the  middle  lobe,  developed  from  the  middle  plate, 
which,  in  the  incisors,  is  the  smallest  of  the  three,  but  in  this 
tooth  is  much  the  largest.  There  are  two  labial  furrows  {e), 
or  a  flattening  of  the  convexity  between  the  central  line  of  the 
ridge  and  each  angle,  marking  the  junction  of  the  lobes.  These 
furrows  are  usually  lost  by  becoming  shallower  before  reaching 
the  center  of  the  length  of  the  crown.  In  well-formed  teeth, 
this  surface  presents  a  uniform  enamel,  free  from  pits  or  sulci. 

-'  34.  The  lingual  surface  (Fig.  19)  presents  the  same 
general  marginal  configuration  as  the  labial,  though  it  is  some- 
what narrower  toward  the  gingival  line.;  This  is  caused  by  the 
arc  of  convexity  of  the  lingual  surface  of  the  neck  of  the  tooth 
being  of  a  smaller  circle  than  that  of  the  labial,  and  by  the  flat- 


38  THE    UPPER    CUSPID. 


tening  of  the  proximate  surfaces  on  lines  which  converge  rap- 
idly to  the  lingual.  This  surface  is  usually  almost  straight 
from  the  cusp  to  the  linguo-gingival  ridge,  or  cingulum,  but  is 
sometimes  slightly  concave.  The  linguo-gingival  ridge  is 
sharply  convex  and  longer  from  the  gingival  line  to  the  point 
of  convexity  than  in  the  incisors.  (Fig.  21,  d.)  Mesio-distally 
this  surface  is  slightly  convex  in  its  central  part  on  account  of 
the  lingual  ridge  which  runs  from  the  point  of  the  cusp  nearly, 
or  quite,  to  the  cingulum.  On  each  side  of  this,  and  between  it 
and  the  marginal  ridges,  there  is  a  slight,  but  well-defined  con- 
cavity and  furrow,  marking  the  confluence  of  the  lobes.  The 
marginal  ridges  arise  from  the  mesio-  and  disto-incisal  angles 
and  unite  with  the  linguo-gingival  ridge  or  cingulum.  These 
ridges  are  usually  large  near  the  angles,  and  much  less  pro- 
nounced toward  the  linguo-gingival  ridge.  The  latter  is  promi- 
nent, and  is  often  raised  into  a  tubercle,  or  slight  cusp.  Occa- 
sionally this  part  of  the  enamel  is  thrown  into  irregular  folds, 
with  grooves  between,  which  are  sometimes  fissured.  ;  More 
rarely  the  small  cusp  may  be  divided  by  a  groove  (Fig.  20,  n). 
The  linguo-gingival  groove  is  often  pronounced  in  unworn 
teeth. 

35.  The  mesial  surface,  near  the  incisal  angle  (Fig. 
21),  is  convex  in  all  directions,  but  becomes  flattened,  and  occa- 
sionally slightly  concave,  near  the  gingival  line  (c). 

36.  The  distal  surface  is  similar  to  the  mesial,  but  is 
more  convex,  usually  being  well  rounded  in  the  lablo-lingual 
direction  to  the  gingival  line./  But  in  the  direction  of  the  long 
axis  of  the  tooth  this  surface,  on  account  of  its  distal  projection 
is  first  convex,  and  further  toward  the  gingival  line  is  concave, 
especially  near  and  at  the  neck  of  the  tooth.  The  labio-lingual 
curvature  of  the  gingival  line  is  about  2.5  m.m.,  varying  from 
i.o  m.m.  to  3.5  m.m.  on  the  mesial  surface,  and  a  little  less  on 
the  distal. 

37.  The  root  of  the  upper  cuspid  is  the  longest  in  the 
human  mouth,  averaging,  according  to  my  measurements,  17.5 


Fig.  29. 


Fig.  25*  (Par.  38). — Left  Lower  Cuspid,  Labial  Surface,     a.   Point  of  cusp; 

b,  mesial  surface;  c,  distal  surface;  d,  labial  ridge;  e,  distal  labial  groove;  /,  gingi- 
val line;  g,  mesio-incisal  angle;  /;,  disto-incisal  angle;  t,  body  of  root;  k,  apex  of 
root. 

Fig.  26*  (Par.  38). — Left  Lower  Cuspid,  Mesial  Surface,  a,  Point  of  cusp; 
d,  linguo-gingival  ridge;  f,  gingival  line;  g,  mesio-incisal  angle;  i,  body  of  root, 
which  is  distinctly  flattened;   k,  apex  of  root. 

Fig.  27*  (Par.  38). — Left  Lower  Cuspid,   Distal  Surface,    a,  Point  of  cusp; 

c,  labial  groove;  d,  linguo-gingival  ridge;  e,  concavity  of  the  distal  cutting  edge 
where  the  groove  passes  over  it;  /,  gingival  line;  h,  disto-incisal  angle;  i,  body  of 
root;   k,   apex   of   root. 

Fig.  28*  (Par.  39). — Left  Lower  Cuspid,  Lingual  Surface,    a.  Point  of  cusp; 

d,  linguo-gingival  ridge;  c,  lingual  grooves;  /,  gingival  line;  g,  mesio-incisal  angle; 
h,  disto-incisal  angle j  i,  body  of  root;  k,  apex  of  root;  /,  distal  marginal  ridge;  m, 
lingual    or   triangular   ridge;   n,    mesial    marginal    ridge. 

Fig.  29*  (Par.  40). — Right  Lower  Cuspid,  Mesial  Surface,  a,  Point  of  cusp; 
d,  linguo-gingival  ridge;  /,  gingival  line;  g,  mesio-incisal  angle.  The  root  is  short 
and   thick. 


*IIlustration,    lYz  diameters. 


THE  LOWER  CUSPIDS.  4I 

m.m.,  and  varying  from  ii.o  to  21.0  from  the  apex  to  the  gin- 
gival line  at  the  labial  surface.  It  is  irregularly  conical  in 
form,  tapering  from  the  neck  to  the  apex.  Its  labio-lingual 
diameter  is  a  little  greater  than  its  mesio-distal,  which  gives 
the  root  a  flattened  appearance,  but  it  is  seldom  entirely  flat  on 
either  the  mesial  or  distal  surface.  In  most  examples  the  body 
of  the  root  is  straight,  and  tapers  to  a  slender  point,  which  is 
often  curved  to  the  labial  and  distal,  though  the  form  of  this 
root  presents  great  variations.  Frequently,  it  is  very  crooked, 
perhaps,  because,  when  it  is  taking  its  place  in  the  arch,  it  is 
often  crowded  by  the  teeth  mesial  and  distal  to  it,  so  that  its 
growth  in  a  right  line  is  interrupted.  (See  Figs.  22,  23, 
and  24.) 

THE  LOWER  CUSPIDS. 

38.  In  their  general  figure,  the  lower  cuspids  so  closely 
resemble  the  upper,  a  description  of  their  differences  will  be 
sufficient.  They  are  slightly  smaller  than  the  upper  cuspids, 
and  the  crowns  are  a  little  longer,  which  make  them  appear 
more  slender.  The  mesial  surface  of  these  teeth  is  usually 
nearly  straight  the  entire  length  of  the  root  and  crown  (Figs. 
25  and  26)  ;  so  that  the  increased  width  of  the  crown  over  the 
root  is  mainly  on  the  distal.  This  causes  a  marked  prominence 
of  the  disto-incisal  angle.  In  many  examples  this  gives  the 
tooth  the  appearance  of  being  bent,  with  a  considerable  con- 
cavity on  the  distal  side  in  the  cervical  region: ;  In  young,  un- 
worn teeth,  the  cusp  is  rather  more  prominent  and  pointed  than 
in  the  upper  cuspid,  and  the  distal  cutting  edge  is  proportion- 
ately longer;  but,  as  the  point  of  the  cusp  comes  directly  in 
occlusion  with  the  upper  teeth,  it  is  soon  worn  to  a  blunt  point, 
or  a  flat  surface,  inclining  to  the  labial  and  sloping  away  to  the 
distal. 

39.  The  lingual  surface  (Fig.  28)  is  very  smooth,  and 
the  ridges  are  less  prominent  than  in  the  upper  cuspid.  A 
tubercle  on  the  linguo-gingival  ridge  is  rare.  The  develop- 
mental lines,  or  grooves,  are  the  same  as  those  of  the  upper 


42  THE  BICUSPIDS. 


cuspids,  but  less  prominent.  Yet,  generally,  they  can  be  seen 
in  unworn  teeth.  Fissures  are  seldom  seen  in  any  part  of  this 
tooth. 

40.  The  root  of  the  lower  cuspid  (Figs.  25  to  29)  is 
shorter  than  the  upper,  and  generally  more  flattened  in  the  me- 
sio-distal  diameter,  often  presenting  deep  furrows.  In  rare  in- 
stances, there  is  a  division  of  the  root  near  the  extremity.  The 
root  is  nearly  straight,  and  in  many  examples  the  lingual  sur- 
face of  the  root  is  nearly  a  straight  line,  while  the  labial  sur- 
face, root,  and  crown,  present  a  nearly  regular  convexity.  The 
root  is  not  so  often  abnormally  crooked  as  that  of  the  upper 
cuspid,  though,  like  the  upper,  it  is  much  inclined  to  end  in  a 
slender  apex,  which  is  often  slightly  bent  in  the  labial  direction! 

THE   BICUSPIDS. 

41.  There  are  eight  bicuspids,  or  premolars,  two  on  each 
side  in  the  upper  jaw,  and  two  on  each  side  in  the  lower  jaw. 
Hence  they  are  called  the  first  and  second  bicuspids.  They 
are  situated  between  the  cuspids  and  first  molars,  and  are  the 
fourth  and  fifth  teeth  from  the  median  line.  The  bicuspids, 
though  unlike  the  incisors  and  cuspids  in  the  contour  of  their 
crowns,  have  the  same  number,  and  a  similar  distribution  of 
primary  parts,  or  lobes.  They  are,  indeed,  formed  on  the 
same  general  plan.  The  change  of  form  is  the  result  of  a 
different  relative  development  of  the  parts,  by  which  the  cingu- 
lum,  or  linguo-gingival  ridge,  is  elevated  into  a  powerful 
lingual  cusp,  which,  in  the  upper  bicuspids,  is  almost  or  quite 
as  'high  as  the  buccal  cusp,  but  in  the  lower  bicuspids,  espe- 
cially in  the"  first,  is  less  prominent.  The  middle  lobe  also  forms 
a  relatively  larger  part  of  the  buccal  portion  of  the  crown  than 
in  the  incisors  and  cuspids ;  while  the  mesial  and  distal  lobes 
are  relatively  smaller.  By  the  development  of  the  lingual  cusp 
of  the  upper  bicuspids,  the  linguo-gingival  grooves  of  the  in- 
cisors and  cuspids  {q.v.21)  are  carried  to  the  central  part  of  the 
crown,  which  they  traverse  from  mesial  tadistal  in  a  deep  sulcus 
(Fig.  30).     It  is  naturally  divided,  by  the  mesial  and  distal  pits 


Fig.  30- 


Fig-  33- 


/> 


Fig.  34- 


Fig.  30*  (Par.  42). — Left  Upper  First  Bicuspid,  Occlusal  Surface.  a. 
Point  of  buccal  cusp;  6,  lingual  cusp;  c,  buccal  ridge;  d,  mesial  marginal  ridge;  e, 
distal  marginal  ridge;  f,  triangular  ridge  of  the  buccal  cusp;  g,  disto-bucco-occlusal 
angle;  h,  mesio-buccal  occlusal  angle;  i,  triangular  ridge  of  the  lingual  cusp;  /,  cen- 
tral groove;  0,  mesial  groove;  p,  distal  groove;  ",  m,  triangular  grooves;  r,  s, 
buccal  grooves. 

Fig.  31*  (Par.  46).— Left  Upper  First  Bicuspid,  Buccal  Surface,  o.  Buccal 
cusp;  c,  buccal  ridge;  e,  e,  buccal  grooves;  f,  gingival  line;  g,  mesio-bucco-occlusal 
angle;  h,  disto-bucco-occkisal   angle;   /,   buccal  root;   k,   lingual   root. 

Fig.  32*  (Par.  48). — Right  Upper  First  Bicuspid,  Mesial  Surface,  a,  Buccal 
cusp;  b,  lingual  cusp;  c,  mesio-buccal-occlusal  angle;  d,  mesial  surface  and  point 
where  there  is  often  a  concavity;  /,  /,  gingival  line;  e,  lingual  root;  g,  buccal  root. 

,     Fig.    33*    (Par.    50).— Upper    First    Bicuspid,    with    three    roots.      Mesio-buccal 
angle. 

Fig.  34*  (Par.  50). — Upper  First  Bicuspid,  with  three  short  roots  and  of  a 
peculiar  form. 

Fig.  35*  (Par.  5c). — Upper  First  Bicuspid,  with  a  single,  very  long,  crooked 
root. 


Illustration,    i>4   diameters. 


UPPER  FIRST  BICUSPID.  45 

found  at  its  junction  with  the  triangular  grooves,  into  three 
parts:  mesial  (o),  central  (/),  and  distal  (p).  In  the  lower 
bicuspids  the  lingual  lobe  is  often  very  small  and  the  course  of 
the  grooves  irregular. 

UPPER  FIRST  BICUSPID. 

42.  The  outline  of  the  occlusal  surface  of  the  upper 
first  bicuspid  (Fig.  30),  when  seen  in  a  line  with  the  long  axis 
of  the  tooth,  is  irregularly  quadrilateral  or  trapezoidal,  in  form. 
The  bucco-lingual  diameter  is  about  two-ninths  greater  than 
the  mesio-distal.  The  flattened  proximate  surfaces  converge 
toward  the  lingual,  so  that  the  mesio-distal  measurement  of 
the  buccal  portion  is  a  little  greater  than  the  lingual.  The 
buccal  and  lingual  margins  are  convex.  The  buccal  convexity 
forms  an  arc  of  about  a  quarter  circle,  and  merges  into  the 
proximate  surfaces  by  obtuse,  but  well-defined,  angles  (h,  g). 
The  lingual  margin  forms  an  arc  of  nearly  half  a  circle,  and 
merges  into  the  proximate  margins  without  any  angular 
prominence. 

43.  The  occlusal  surface  has  two  prominent  cusps — the 
buccal  (a)  and  the  lingual  (b) — and  is  transversed  from  mesial 
to  distal  by  a  deep  sulcus.  The  buccal  cusp  is  the  larger, 
and  forms  the  terminal  point  of  the  buccal  surface.  From  the 
point  of  this  cusp,  four  ridges  lead  away  at  right  angles.  Two 
of  these  form  cutting  edges,  which  slope  away  mesially  and 
distally  to  the  mesio-bucco-occlusal  (h)  and  disto-bucco-occlu- 
sal  angles  (g),  where  they  join  the  mesial  and  distal  marginal 
ridges.  The  central  buccal  ridge  (c)  leads  away  centrally  on 
the  buccal  surface  toward  the  gingival  line,  forming  the  con- 
vexity of  this  surface.  The  triangular  ridge  (f)  slopes  down 
to  the  central  part  of  the  crown  and  joins  a  similar  ridge  from 
the  lingual  cusp  (i)  to  form  the  transverse  ridge,  or  ends  in  a 
central  sulcate  groove  (/).  The  lingual  cusp  (&)  is  in  the 
form  of  a  crescent ;  its  convexity  forms  the  occlusal  margin  of 
the  lingual  surface.  Instead  of  a  well-defined  point  it  usually 
presents  a  blunt  edge,  which  runs  around  its  elevated  central 


46  UPPER  FIRST  BICUSPID. 

"portion,  and  joins  with  the  marginal  ridges  at  both  angles.  The 
lingual  triangular  ridge  (i)  leads  down  from  the  central  point 
of  the  cusp  to  the  central  groove,  to  join  its  fellow  from  the 
buccal  cusp  in  the  formation  of  the  transverse  ridge,  or  is 
divided  from  it  by  a  deep  central  sulcate  groove.  This  ridge 
is  seldom  prominent.  Very  frequently  the  central  incline  of 
the  lingual  cusp  is  a  plain  surface. 

44.  The  mesial  (d)  and  the  distal  (e)  marginal  ridges 
are  strong  ridges  of  enamel  which  rise  in  the  mesial  and  distal 
terminations  of  the  cutting  edges  of  the  buccal  cusp,  and  form 
the  mesial  and  distal  margins  of  the  occlusal  surface.  They 
join  with  the  ridge  forming  the  lingual  cusp,  or  they  are  usu- 
ally divided  from  the  latter  by  the  mesial  and  distal  grooves, 
though  these  grooves  are  often  indistinct,  especially  in  teeth 
that  have  been  somewhat  worn. 

45.  The  occlusal  surface  of  the  bicuspids  has  five  de- 
velopmental grooves — the  central  (/),  mesial  (0),  distal  (p), 
mesial  triangular  (;n),  and  distal  triangular  (n).  The  cen- 
tral groove  is  deeply  sulcate,  and  divides  the  triangular  ridges, 
or  passes  over  their  junction  as  a  shallow  line,  and  sinks  into 
a  triangular  pit  at  either  end.  The  mesial  and  distal  grooves 
are  really  continuations  of  the  central,  which  pass  over  the 
marginal  ridges  as  very  fine  lines,  or  as  more  definite  grooves, 
and  mark  the  boundary  of  the  lingual  lobe.  They  are  rarely 
fissured,  while  the  central  groove  is  frequently  fissured  through- 
out its  course.  The  triangular  grooves,  mesial  (w)  and  distal 
(w),run  from  the  mesial  and  distal  pits  toward  the  mesio-buccal 
and  disto-buccal  angles,  dividing  the  marginal  ridges  from  the 
triangular.  They  are  occasionally  sulcate  in  the  first  part  of 
their  course,  and  are  generally  lost  toward  the  mesio-  and  disto- 
buccal  angles  by  becoming  shallower;  but  in  young,  unworn 
teeth  they  can  often  be  followed  as  a  fine  line  running  over  the 
cutting  edges  of  the  buccal  cusp  near  the  angles,  and  leading 
into  the  buccal  grooves  (r,  s).  These  are  the  marks  of  con- 
fluence of  the  mesial  and  distal  lobes  with  the  middle  lobe.  In 
the  central  incline  of  the  lingual  cusp,  supplemental  grooves 
are  often  seen  meeting  the  triangular  grooves  of  the  buccal 


Fig.  36. 


^ 


Fig.  39. 


Fig.  41. 


Fig.  2(>*  (Par.  51). — Right   Upper   Second    Bicuspid,    Occlusal    Surface,     a, 

oint  of  buccal  cusp;  b,  lingtial  cusp;  c,  buccal  ridge;  e,  mesial  marginal  ridge;  d, 

distal  marginal  ridge ;  /,  triangular  ridge  of  the  buccal  cusp ;  g,  mesio-bucco-occlu- 

sal  angle;   /;,   disto-bucco-occlusal  angle;   i,  triangular  ridge  of  the  lingual  cusp;   /, 

central   groove;   m,   n,   triangular   grooves;   0,  p,  buccal   grooves. 

Fig.  37*  (Par.  52). — Right  Upper  Second  Bicuspid,  Buccal  Surface.  a, 
Point  of  buccal  cusp;  c,  buccal  ridge;  e,  e,  buccal  grooves;  f,  gingival  line;  g, 
mesio-bucco-occlusal  angle;  h,  disto-bucco-occlusal  angle;  i,  body  of  root;  k,  apex 
of    root. 

Fig.  3S*  (Par.  52). — Right  Upper  Second  Bicuspid,  Mesial  Surface,  a. 
Buccal  cusp;  b,  lingual  cusp;  /,  gingival  line;  i,  groove  in  the  mesial  side  of  the 
root. 

Fig.  39*  (Par.  52). — Right  Upper  Second  Bicuspid,  Distal  Surface,  a. 
Buccal  cusp;  b,  lingual  cusp;  c,  carious  cavity  near  the  proximate  contact  point;  /, 
gingival  line;  i,  groove  in  distal  side  of  root. 

Fig.  40*  (Par  53). — Upper  Second  Bicuspid,  with  a  very  crooked  root. 

Fig.  41*  (Par.  53). — Upper  Second  Bicuspid,  with  a  very  short  crook  of  the 
root. 


*Illustration,    lYz   diameters. 

5 


UPPER  FIRST  BICUSPID.  49 

side.     The  triangular  grooves  are  occasionally  fissured  for  a 
short  distance  from  their  junction  with  the  central. 

46.  The  buccal  surface  of  the  upper  first  bicuspid 
(Fig.  31)  is  similar  to  the  labial  surface  of  the  cuspid  (g.  e^.  33). 
The  cusp  is  usually  nearer  the  center  of  the  crown,  and  gen- 
erally somewhat  to  the  distal ;  therefore,  the  cutting  edges 
which  run  from  the  summit  of  the  cusp  to  either  angle  may  be 
of  about  equal  length.  In  some  examples  the  distal  edge  is 
the  longer ;  but  usually  the  mesial  edge  is  the  longer.  In  the 
gingival  half  of  its  length  this  surface  is  smoothly  convex  from 
mesial  to  distal ;  but  further  toward  the  occlusal  margin,  the 
buccal  ridge,  which  terminates  in  the  cusp,  becomes  more 
prominent,  and  a  shallow  buccal  groove  {e,  e)  appears  at  both 
sides  of  the  ridge,  or  between  it  and  the  angles.  This  surface 
is  also  considerably  narrowed  toward  the  gingival  margin,  al- 
most equally  on  the  mesial  and  distal,  so  that  the  crown  seems 
much  broader  near  the  occlusal  margin. 

47.  The  lingual  surface  is  regularly  convex  from  me- 
sial to  distal.  From  the  gingival  margin  to  the  summit  of  the 
lingual  cusp  it  is  often  a  straight  line ;  but  more  generally  it  is 
slightly  convex,  in  many  examples  almost  as  convex  as  the 
buccal  surface. 

48.  The  mesial  surface  (Fig.  32)  is  jnuch  flattened 
from  buccal  to  lingual,  but  is  generally  slightly  coriv^x  over  its 
whole  extent ;  yet  in  many  examples  there  is  a  slight  concavity 
nearJh£^.ging|yaJJirie,  In  the  direction  from  the  gingival  lTne~ 
to  the  occlusal  margin,  this  surface  is  sliglitly  convex  through 
its  whole  length,  but  not  equally  so  through  its  buccal  and 
lingual  half.  The  lingual  portion  is  progressively  njii^e 
roijnded  toward  the  occlusaT~surface ;  while  the  buccal  portion 
Ts^nearly^straight  to  the  bucco-occlusal  angle.* 

*  The  form  of  the  proximate  surfaces  is  especially  important  in 
making  contour  fillings,  for  any  concavity  increases  the  difficulty  of 
forming  good,  clean  margins  at  the  gingival  border.  The  unequal 
convexity  of  the  buccal  and  lingual  halves  is  important,  and  requires 
a  special  adaptation  of  instruments  to  make  a  perfect  contour  and 
good,  clean  margins. 


50  UPPER   SECOND   BICUSPID. 

49.  The  form  of  the  distal  surface  agrees  substantially 
with  the  mesial,  but  is  rather  more  convex  in  all  directions  and 
aiivcon^avity  isj;are^ 

50.  The  root  of  the  upper  first  bicuspid  is  usually  either 
much  flattened  and  grooved  on  its  mesial  and  distal  sides,  or 
separated  into  two  divisions,  one-third  to  two-thirds  of  its 
length,  making  one  buccal  and  one  lingual  root.  More  than 
half  have  their  roots  thus  divided.  When  separated,  the  roots 
taper  regularly  to  slender  apexes.  When  not  divided,  the 
apex  is  apt  to  be  obtuse.  Occasionally  this  tooth  presents 
three  divisions  of  the  root,  two  buccal  and  one  lingual  (Figs. 
33,  34).  In  some  instances  the  root  of  this  tooth  is  very 
crooked  or  otherwise  distorted  (Fig.  35). 

UPPER  SECOND  BICUSPID. 

51.  The  upper  second  bicuspid  so  nearly  resembles  the 
upper  first,  just  described,  that  a  notice  of  its  differences  will 
be  sufficient.  It  is  a  little  smaller,  and  in  every  way  more 
slender.*  The  general  form  of  the  occlusal  surface  (Fig. 
36)  is  similar  to  the  first  bicuspid.  It  presents  a  buccal  and  a 
lingual  cusp,  and  similar  sulcus,  ridges,  grooves,  and  pits. 
The  average  height  of  the  cusps  is  considerably  less  than  in  the 
first  bicuspid.  The  marginal  ridges  are  proportionally  broader, 
the  mesial  and  distal  pits  closer  to  each  other,  and  the  central 
groove  shorter.  The  triangular  grooves  join  the  central 
groove  nearer  the  mesio-distal  center  of  the  tooth,  making  the 
buccal  triangular  ridge  narrower  and  more  nearly  pointed.  In 
many  examples  the  enamel  of  the  occlusal  surface  is  thrown 
into  several  shallow  wrinkles,  or  sugpkmental  grooves  and 
ridges,  which  radiate  from  the  central  groove,  which  occurs 
but  rarely  in  the  first  bicuspid.  The  buccal  cusp  is  a  little 
nearer  the  mesio-buccal  than  the  disto-buccal  angle,  so  that  the 
distal  edge  is  slightly  the  longer. 

52.  From  mesial  to  distal,  the  buccal  surface  (Fig.  37) 
is  not  so  broad  at  the  occlusal  surface,  and  is  a  little  broader 

*The  popular  opinion  is  that  the  second  bicuspid  is  the  larger. 


Fig.  42. 


Fig.  45- 


Fig.  46. 


Fig.  47- 


Fig.  42*  (Par.  54). — Right  Lower  First  Bicuspid,  Occlusal  Surface,  c, 
Point  of  buccal  cusp;  b,  lingual  cusp  or  ridge;  c,  buccal  ridge;  d,  mesial  marginal 
ridge;  c,  distal  marginal  ridge;  /,  triangular  ridge  of  buccal  cusp  or  buccal  triangu- 
lar ridge;  g,  mesio-bucco-occlusal  angle;  h,  disto-bucco-occlusal  angle;  i,  central 
groove  crossing  the  transverse  ridge;  /,  mesial  pit;  0,  p,  buccal  grooves. 

Fig.  43*  (Par.  54). — Lower  First  Bicuspid,  Occlusal  Surface,  a,  Point  of 
buccal  cusp;  b,  lingual  cusp  or  ridge;  c,  triangular  ridge  of  buccal  cusp  deflected  to 
one  side;  d,  triangular  groove  with  fissure;  c,  mesial  marginal  ridge;  /,  distal  mar- 
ginal ridge. 

Fig.  44*  (Par.  57). — Right  Lower  First  Bicuspid,  Buccal  Surface,  a,  Buc- 
cal cusp;  d,  buccal  ridge;  e,  e,  buccal  grooves;  /,  gingival  line;  g,  disto-bucco- 
occlusal  angle;  h,  mesio-bucco-occlusal  angle;  t,  body  of  root;  k,  apex  of  root. 

Fig.  45*  (Par.  58). — Left  Lower  First  Bicuspid,  Mesial  Surface,  a,  Buc- 
cal cusp;  b,  lingual  cusp  or  ridge;  c,  distal  marginal  ridge;  d,  triangular  ridge  of 
buccal  cusp;  e,  mesial  marginal  ridge;  /,  gingival  line. 

,  ^  Fig.  46*  (Par.  59). — Left  Lower  First  Bicuspid,  Lingual  Surface.  a, 
Buccal  cusp;  b,  lingual  cusp  or  ridge;  c,  distal  marginal  ridge;  d,  triangular  ridge 
of  buccal  cusp;  e,   mesial  marginal  ridge;    f,   gingival   line. 

Fig.  47*  (Par.  59). — Right  Lower  First  Bicuspid,  Lingual  Surface,  a,  Buc- 
cal cusp;  b,  lingual  cusp  or  ridge;  d,  triangular  ridge  or  buccal  cusp;  e,  e,  mar- 
ginal  ridges;    /,   gingival   line. 


"■Illustration,   i^   diameters. 


LOWER  FIRST  BICUSPID.  53 

at  the  neck,  so  that  it  has  not  so  much  of  the  bell-crown  ap- 
pearance as  the  first  bicuspid.  Otherwise,  this  surface  has  the 
same,  but  less  definitely  defined  outlines  and  markings.  The 
mesial  and  distal  surfaces  (Figs.  38  and  39)  are  generally 
slightly  more  convex,  and  the  crown  more  smoothly  rounded. 
The  mesial  surface  seldom  shows  a  concavity.  The  lingual 
surface  is  usually  a  little  more  rounded  toward  the  cutting 
edge  or  crest  of  the  cusp.  Generally,  the  distal  side  of  the 
lingual  cusp  is  rounded  to  such  an  extent  as  to  bring  the  sum- 
mit of  the  cusp  to  the  mesial  of  the  central  line  of  the  tooth. 
The  gingival  line,  in  its  course  round  the  neck  of  the  tooth, 
makes  but  a  slight  bucco-lingual  curvature  on  the  mesial  sur- 
face.   Generally  there  is  no  curvature  on  the  distal  surface. 

53.  The  root  of  the  upper  second  bicuspid  is  a  little 
longer  than  the  first,  while  the  crown  is  slightly  shorter, 
which  makes  the  proportionate  increase  of  length  appear 
considerable.  The  root  is  rarely  divided  in  any  part  of  its 
length,  but  is  much  flattened  from  the  neck  to  the  apex. 
The  mesial  side  is  often  deeply  grooved  in  the  apical  third 
of  its  length;  the  distal  side  is  less  frequently  grooved.  The 
root  tapers  very  gradually,  remaining  broad  in  the  bucco- 
lingual  diameter,  and  ends  in  a  blunt  apex.  A  few  have  a 
root  that  tapers  rapidly,  becomes  more  rounded,  and  ends  in 
a  slender  apex.  Crooked  roots  are  more  frequent  in  this  than 
in  the  other  bicuspids.     (Figs.  40  and  41.) 

LOWER  FIRST  BICUSPID. 

54.  This  tooth  is  the  smallest  of  the  bicuspids.  The 
occlusal  surface  differs  much  from  the  upper  first  bicuspid. 
Indeed,  the  lingual  cusp  is  so  nearly  wanting,  it  would  hardly 
be  called  a  bicuspid  except  for  its  association.  The  buccal 
cusp  is  large  and  prominent,  and  so  much  is  the  buccal  surface 
inclined  lingually,  that,  when  seen  in  a  line  with  the  long  axis 
of  the  tooth,  its  point  occupies  a  position  about  one-third 
distant  from  the  buccal  toward  the  lingual  outline  of  the 
crown  (Figs,  42  and  43).    The  buccal  cusp  presents  the  same 


54  LOWER  FIRST  BICUSPID. 

ridges  leading  from  its  summit  as  described  for  the  upper 
first  bicuspid  (Par.  43),  but  the  pair  which  form  the  cutting 
edges  usually  form  a  curve  with  its  convexity  to  the  buccal, 
and  merge  into  the  marginal  ridges  by  more  rounded  angles. 
The  buccal  triangular  ridge  is  narrow  and  prominent  (/),  and 
joins  the  elevated  lingual  ridge,  or  cusp  (b),  forming  a  com- 
plete transverse  ridge.  In  many  instances  this  is  deflected 
to  the  mesial  or  distal.  In  young  teeth,  the  central  groove 
often  crosses  the  transverse  ridge  as  a  fine  line,  which  soon 
disappears  by  wear.  However,  in  many  examples  the  trans- 
verse ridge  is  divided  by  a  deeply  sulcate  groove.  There  is  a 
deep  pit  at  the  mesial  and  the  distal  ends  of  the  central  groove, 
or  on  either  side  of  the  transverse  ridge  (c,  d)  from  which  the 
triangular  grooves,  which  divide  the  marginal  ridges  from 
the  triangular,  or  transverse  ridge,  run  toward  the  mesio-  and 
disto-buccal  angles.  These  are  often  sulcate  in  the  first  part 
of  their  course.  In  many  young  teeth  these  grooves  may  be 
traced  over  the  cutting  edges  onto  the  buccal  surface,  marking 
the  confluence  of  the  central  with  the  mesial  and  distal  buccal 
lobes. 

55.  The  lingual  lobe  varies  much  in  its  size  and  out- 
line. It  is  divided  from  the  three  buccal  lobes  by  the  mesial, 
distal,  and  central  grooves ;  and  often  occupies  but  a  small 
portion  of  the  lingual  margin  of  the  occlusal  surface.  The 
grooves  which  mark  its  outlines  are  often  indistinct,  and  often 
obliterated  by  wear.  The  lobe  may  form  a  ridge  of  even 
height,  and  join  the  marginal  ridges,  or  it  may  be  elevated 
into  one  or  more  tubercles.  It  may,  also,  be  raised  into  a 
small  cusp,  located  centrally,  or  to  either  side  of  the  central 
line  of  the  tooth. 

56.  The  marginal  ridges  are  occasionally  quite  small, 
but  in  most  examples  they  are  well  developed,  and  cause  the 
mesial  and  distal  surfaces  to  stand  out  prominently,  giving 
the  tooth  a  strong,  bell-crowned  appearance.  The  length  of 
the  marginal  ridges  varies  with  the  size  of  the  lingual  lobe. 

57.  The  buccal  surface  (Fig.  44)  is  convex  in  all  direc- 


LOWER   FIRST  BICUSPID.  55 

tions.  The  cusp  is  to  the  distal  of  the  perpendicular  line  and 
its  figure  similar  to  the  upper  first  bicuspid,  except  that  its 
surface  is  more  convex.  As  the  occlusion  is  directly  on  the 
point  of  the  cusp,  as  with  the  anterior  lower  teeth  generally, 
it  is  soon  so  worn  down  that  its  prominence  is  lost. 

58.  The  mesial  and  distal  surfaces  are  convex  from 
buccal  to  lingual.  In  the  direction  from  the  occlusal  margin 
to  the  gingival  line,  they  are  generally  concave,  after  passing 
the  convexity  of  the  immediate  occlusal  margin.  This  latter 
stands  out  boldly  to  both  mesial  and  distal,  giving  a  marked 
bell-crowned  form.  The  concavity  of  the  mesial  and  distal 
surfaces  is  not  so  well  seen  from  the  buccal  view  as  from  the 
lingual.  The  greater  over-hang  of  the  crown  (over  the  root), 
and  the  greater  concavity,  are  toward  the  lingual  portion. 

59.  The  lingual  surface  (Figs.  46  and  47)  is  smoothly 
rounded  from  mesial  to  distal,  and  slightly  convex  in  the 
direction  of  the  length  of  the  tooth.  It  is  only  about  half 
as  long  as  the  buccal  surface  (in  unworn  teeth),  and  when 
viewed  at  right  angles  with  the  long  axis  of  the  tooth,  all  of 
the  occlusal  surface  on  the  lingual  side  of  the  buccal  cusp  is 
seen  except  the  pits  and  sulci. 

60.  The  neck  of  the  tooth  is  much  constricted,  and  has 
a  deep  gingival  line.  This  makes  the  proper  adjustment  of 
a  band  for  an  artificial  crown  particularly  difficult.  The 
curvature  of  the  gingival  line  is  much  less  than  in  the  upper 
first  bicuspid,  the  average  being  less  than  one  millimeter  (g.  v. 
table  of  measurements). 

61.  The  root  of  this  tooth  is  somewhat  flattened  at  the 
neck,  on  lines  that  converge  rapidly  toward  the  lingual,  and 
often  grooved  on  its  mesial  and  distal  sides,  and  sometimes 
the  root  is  bifurcated.  It  tapers  regularly,  with  a  tendency 
to  a  more  nearly  round  form  at  the  apex,  and  generally  ends 
in  a  slender  point.  The  root  is  generally  straight,  or  the 
lingual  surface  is  straight,  and  the  buccal  surface  convex. 
This  convexity  extends  from  the  apex  of  the  root  to  the  point 
of  the  crown,  which  gives  that  characteristic  appearance  so 
peculiar  to  the  anterior  lower  teeth. 


56  LOWER  SECOND  BICUSPID. 

LOWER  SECOND  BICUSPID. 

62.  The  lower  second  bicuspid  is  a  little  longer  than 
the  lower  first,  and  of  much  the  same  figure,  except  that  the 
lingual  cusp  is  proportionately  higher  and  more  nearly,  but 
never  quite,  on  a  level  with  the  buccal,  but  the  lingual  surface 
is  about  equal  to  the  buccal  in  mesio-distal  breadth.  These 
teeth  are  regular  in  general  contour,  but  the  grooves  of  the 
occlusal  surface  are  much  diversified.  /  These  differences  may 
be  classified  under  three  forms:  ist.  The  central  groove 
joins  the  triangular  grooves  in  such  a  way  as  to  form  a  half 
circle  with  the  convexity  to  the  lingual,  with  or  without  a 
transverse  ridge  crossing  its  line.  In  these,  when  the  trans- 
verse ridge  is  high,  only  a  deep  pit  appears  on  either  side 
(Fig.  48).  2d.  The  lingual  cusp  is  divided  by  a  sulcate 
groove,  which  runs  over  centrally,  or  nearly  so,  to  the  lingual 
surface,  making  a  three-cusped  tooth  (Fig.  49),  The  central 
groove  forms  an  angle  at  the  junction  with  the  lingual,  or  is 
crescentic  in  form.  It  joins  with  the  triangular  grooves  in 
such  a  way  that  the  point  of  junction  cannot  be  told  except 
by  finding  the  mesial  and  distal  grooves,  which  are  often  very 
indistinct.  3d.  The  central  groove  is  straight,  and  generally 
sulcate,  with  a  deep  pit  at  each  end.  In  many  examples 
these  pits  are  crossed  by  the  triangular  grooves  almost  at 
right  angles  with  the  central  (Fig.  50).  By  tracing  the  fine 
mesial  and  distal  grooves  carefully  in  young  unworn  teeth, 
it  will  be  found  that  the  lingual  lobe  is  much  larger  than  in 
the  lower  first  bicuspid,  and  almost  as  large  as  in  the  upper 
bicuspids.  In  the  three-cusped  forms  the  two  lingual  lobes 
are  usually  a  little  broader  from  mesial  to  distal  than  the 
buccal  portion  of  the  tooth. 

63.  The  buccal  surface  (Fig.  51)  of  the  lower  second 
bicuspid  does  not  differ  from  the  other  bicuspids,  except  in 
being  shorter,  the  cusp  lower.  The  lingual  surface  (Fig.  52) 
is  broader  and  smoothly  convex;  in  the  three-cusped  forms 
it  is  often  somewhat  flattened  and  grooved  in  its  occlusal 
third,  giving  the  crown  a  squarish  appearance,  or  even  trian- 
gular when  the  lingual  lobes  are  large. 


Fig.  4S. 


Fig.  49. 


Fig.  50. 


^.t 


Fig.  51. 


Fig.  52. 


Fig.  53- 


■^ 


Fig.  48*  (Par.  62).— Left  Lower  Second  Bicuspid,  Occlusal  Surface,  a. 
Buccal  cusp;  b,  lingual  cusp  or  ridge;  c:,  c,  marginal  ridges;  d,  f,  pits;  g,  h,  tri- 
angular  grooves. 

Fig.  49*  (Par.  62). — Right  Lower  Second  Bicuspid,  Occlusal  Surface,  with 
three  cusps,  a,  Buccal  cusp;  b,  mesio-lingual  cusp;  c,  disto-lingual  cusp;  d,  lingual 
groove;   e,    c,   mesial   and    distal    grooves. 

Fig.  50*  (Par.  £2). — Right  Lower  Second  Bicuspid,  Occlusal  Surface,  with 
straight  central  groove,  a.  Buccal  cusp;  b,  lingual  cusp;  c,  e,  marginal  ridges;  d, 
triangular  ridge  of  the  buccal  cusp;  f,  central  groove;  g,  h,  triangular  grooves. 

Fig.  si*  (Par.  €3). — Left  Lower  Second  Bicuspid,  Buccal  Surface,  a,  Buc- 
cal cusp;  d,  buccal  ridge;  e,  e,  buccal  grooves;  /,  gingival  line;  g,  mesio-bucco- 
occlusal  angle;  /;,  disto-bucco-occlusal  angle;  i,  body  of  root;  k,  apex  of  root. 

Fig.  52*  (Par.  63). — Left  Lower  Second  Bicuspid,  Lingual  Surface,  a, 
Buccal  "cusp;  b,  lingual  cusp;  c,  distal  marginal  ridge;  d,  triangular  ridge  of  the 
buccal  cusp;  e,  mesial  marginal  ridge;   /,  gingival  line. 

Fig.  S3*  (Par.  64). — Left  Lower  Second  Bicuspid,  Mesial  Surface,  a.  Buc- 
cal cusp; /;,  lingual  cusp;  rf.  triangular  ridge;  e,  mesial  marginal  ridge;  /,  gingival 
line;  i,  groove  in  mesial  side  of  the  root. 


"■Illustration,   ij^   diameters. 


THE  MOLAR  TEETH THE  UPPER  MOLARS.  59 

64.  The  mesial  and  distal  surfaces  in  these  bicuspids 
are  a  little  flattened,  but  remain  convex  from  buccal  to  lingual. 
From  the  occlusal  margin  to  the  gingival  line,  they  are  nearly- 
straight,  though  some  are  convex  and  some  in  part  concave. 
^  65.  The  root  of  the  lower  second  bicuspid  is  larger  and 
longer  than  that  of  the  first  bicuspid.  It  is  flattened  on  the 
mesial  and  distal  surfaces  on  nearly  parallel  lines,  and  in  some 
examples  concave  or  grooved.  In  rare  instances  the  root  of 
this  tooth  is  deeply  grooved  on  the  buccal  and  lingual  sides, 
with  a  tendency  to  a  division  into  a  mesial  and  distal  prong. 
In  the  greater  number  it  tapers  regularly  to  a  'slender  apex, 
but  in  many  the  apex  is  large  and  obtuse.  The  root  is  gen- 
erally straight,  but  occasionally  very  crooked. 

THE    MOLAR   TEETH. 

66.  The  molar  teeth  are  very  different  in  form  and  plan 
of  construction  from  those  previously  described.  They  are 
particularly  designed  for  grinding  or  comminuting  food;  for 
this  purpose  they  have  broad  occlusal  surfaces,  broken  by 
ridges,  grooves,  and  fossae.  The  ridges  are  raised  at  inter- 
vals into  powerful  cusps,  which  fit  with  more  or  less  accuracy 
into  the  sulci  and  fossse  of  the  opposing  teeth.  There  are 
twelve  molars,  three  on  each  side  of  the  upper  jaw  and  three 
on  each  side  of  the  lower  jaw.  They  are  the  sixth,  seventh 
and  eighth  teeth  from  the  median  line,  and  are  commonly 
named  the  first,  second  and  third  molars,  upper  and  lower. 
The  last  is  also  called  the  wisdom  tooth,  or  Dens  Sapientia. 
The  upper  and  lower  molars  are  much  alike  in  size  and  gen- 
eral contour,  but  in  the  detail  of  the  arrangement  of  their 
lobes,  cusps,  fossse  and  grooves,  they  are  different.  /  It  will, 
therefore,  be  necessary  to  describe  the  upper  and  lower  molars 
separately. 

THE  UPPER   MOLARS. 

6^.  The  three  upper  molars  are  similar,  but  present 
minor  differences  of  detail,  consisting  mostly  in  a  less  pro- 
nounced, or  typical  development  of  certain  parts,  or  lobes,  of 
the  second  and  third  molars  (Fig.  62).    The  upper  first  molar 


6o  UPPER  FIRST   MOLAR. 


being  the  typical  form,  will  be  described  first,  and  afterward 
the  deviations  from  this  type  that  occur  in  the  second  and 
third  molars. 

UPPER  FIRST  MOLAR. 

68.  The  occlusal  surface  of  the  upper  first  molar  (Fig. 
54),  when  seen  in  a  line  with  the  long  axis  of  the  tooth,  pre- 
sents an  outline  of  irregular  rhombic  form,  with  the  mesio- 
buccal  and  disto-lingual  as  acute  angles.  The  angles  are 
rounded,  with  more  or  less  convexity  of  the  marginal  lines. 
This  surface  presents  two  principal  fossae,  and  four  develop- 
mental grooves.  These  grooves  divide  the  crown  into  four 
lobes,  or  primary  developmental  parts,  each  of  which  is  sur- 
mounted by  a  strong  cusp.  These  lobes,  or  cusps,  are  the 
mesio-buccal  (Fig.  54,  a),  disto-buccal  (b),  mesio-lingual  (c), 
and  disto-lingual  (d).  Of  the  grooves  which  outline  these 
parts,  three  rise  from  the  central  pit  of  the  central  fossa : 
The  mesial  (h),  which  runs  to  the  mesial  margin;  the  buccal 
(i),  which  runs  in  a  deep  sulcus  to  the  buccal  margin,  and 
over  it  onto  the  buccal  surface;  and  the  distal  (j)^  which 
runs  distally,  and  lingually,  over  the  oblique  ridge  and  ends 
in  the  distal  fossa  (k).  The  remaining  groove — the  disto- 
lingual  (k^  k) — begins  a  little  to  the  buccal  of  the  central  part 
of  the  distal  margin,  and  runs  diagonally  in  a  straight  line, 
or  in  a  curve  with  the  concavity  toward  the  disto-lingual 
angle,  to  the  lingual  margin,  and  over  it  onto  the  lingual 
surface,  to  become  the  lingual  groove.  Except  that  part 
crossing  the  distal  marginal  ridge,  this  groove  is  usually 
deeply  sulcate. 

69.  In  their  origin,  each  lobe  begins  its  calcification  as 
a  separate  piece,  plate,  or  cusp,  and  moves  apart  from  the 
others  as  growth  proceeds,  till  the  proper  dimensions  of  the 
occlusal  surface  are  attained ;  then  the  plates  coalesce  on  the 
lines  marked  by  the  grooves  named  above,  and  thus  complete 
the  occlusal  surface.  When  the  union  has  been  completed, 
nothing  but  fine  lines  remain,  which,  on  any  plain  parts,  are 
often  quickly  obliterated  by  wear.     But  on  parts  meeting  at 


t  X'^^i    { 


Fig.  58. 


Fig.  54*  (Par.  68).— Right  Upper  First  Molar,  Occlusal  Surface,  with  four 
cusps,  a,  Mesio-buccal  cusp;  b,  disto-buccal  cusp;  c,  mesio-lingual  cusp;  d,  disto- 
lingual  cusp;  /,  mesial  m'arginal  ridge;  g,  distal  marginal  ridge;  h,  mesial  groove; 
i,  buccal  groove;  /,  distal  groove  k,  k,  disto-lingual  groove;  m,  mesio-buccal  tri- 
angular groove;  n,  disto-buccal  triangular  ridge;  this  unites  with  the  distal  ridge 
from  the  lingual  cusp  to  form  the  oblique  ridge;  0,  disto-buccal  triangular  groove; 
p,   mesio-buccal   triangular  ridge;    q,   central   pit. 

Fig.  55*  (Par.  70). — Right  Upper  First  Molar,  Occlusal  Surface,  with  five 
cusps,  a,  Mesio-buccal  cusp;  b,  disto-buccal  cusp;  c,  mesio-lingual  cusp;  d,  .disto- 
lingual  cusp;  c,  fifth  cusp;  f,  mesial  marginal  ridge;  g,  distal  'marginal  ridge;  /;, 
mesial  groove;  i,  buccal  groove;  /,  distal  groove;  k,  k,  disto-lingual  groove;  /,  k, 
mesio-lingual  groove;  the  lingual  cusps  are  faceted  by  wear;  m,  mesio-buccal  tri- 
angular groove;  n,  disto-buccal  triangular  ridge. 

— Fig.  56*  (Par.  78). — Right  Upper  First  Molar,  Buccal  Surface,  a,  Mesio- 
buccal  cusp;  b,  disto-buccal  cusp;  c,  mesio-lingual  cusp;  d,  disto-lingual  cusp;  e, 
buccal  ridge;  /,  gingival  line;  g,  mesio-bucco-occlusal  angle;  h,  disto-bucco-occlusal 
angle;  i,  buccal  groove;  k,  mesial  root;  /,  distal  root;  m,  lingual  root. 

Fis.  57*  (Par.  79). — Right  Upper  First  Molar,  Lingual  Surface,  a,  Mesio- 
buccal  cusp;  b,  disto-buccal  cusp;  c,  mesio-lingual  cusp;  d,  disto-lingual  cusp;  e, 
fifth  cusp;  /,  gingival  line;  g,  disto-lingual  groove;  It,  mesio-lingual  groove;  t, 
lingual  groove;  k,  mesial  root;  /,  distal  root;  m,  lingual  root. 

Fig.  58*  (Par.  So). — Right  Upper  First  Molar,  Mesial  Surface,  a,  Mesio- 
buccal  cusp;  b,  disto-buccal  cusp;  c,  mesio-lingual  cusp;  d,  disto-lingual  cusp;  e, 
fifth  cusp;  f,  f,  gingival  line;  h,  mesio-lingual  groove;  k,  mesial  root;  /,  distal  root; 
m,  lingual  root. 


*Illustration,    ij4    diameters. 


UPPER  FIRST  MOLAR.  63 


an  angle,  forming  a  sulcus,  as  in  the  buccal  and  disto-lingual 
grooves,  there  is  usually  a  sharp  groove,  and  at  any  point 
where  the  union  has  been  imperfect,  there  is  a  fissure.* 
Fissures  are  most  frequent  at  the  ends  of  the  grooves,  near 
the  central  pit,  or  where  they  are  deeply  sulcate;  and  in  the 
central  portion  of  the  disto-lingual  groove ;  but  they  may  occur 
in  any  part  of  these  lines. 

70.  In  many  examples  of  the  upper  first  molars,  but  in 
no  others,  there  is  a  small  fifth  lobe  or  cusp  (Fig.  55,  e). 
This  is  situated  on  the  lingual  side  of  the  mesio-lingual  lobe, 
from  which  it  is  divided  by  a  fifth  groove,  the  mesio-lingual 
{I,  ^),  which  runs  from  the  lingual  portion  of  the  mesial  margin 
diagonally  to  the  lingual  margin,  and  joins  the  lingual  groove. 
This  cusp,  when  it  occurs,  is  always  bilateral,  i.  e.,  on  both  the 
right  and  left  upper  first  molars.  It  is  hereditary,  appearing 
regularly  in  the  teeth  of  children  when  present  in  the  teeth  of 
both  parents.  It  occurs  also,  in  a  modified  form,  when  present 
in  but  one  parent.  Therefore,  the  cusp  will  be  found  in  all 
possible  varieties  of  development,  from  its  largest  size,  as  repre- 
sented in  Fig.  55,  to  the  merest  line  marking  its  position  on  the 
lingual  side  of  the  mesio-lingual  cusp. 

-  71.  The  occlusal  surface  of  the  upper  first  molar  has  four 
marginal  ridges,  broken  by  the  grooves  described  (Par.  68), 
so  as  to  form  four  principal  eminences  or  cusps.  These  are 
the  buccal,  lingual,  mesial,  and  distal  marginal  ridges.  Of 
these,  the  mesial  and  distal  marginal  ridges  are  close  upon  the 
margins  of  the  surface.  But  the  buccal  and  lingual  are  carried 
toward  the  central  line  of  the  tooth  by  the  inclination  of  the 
buccal  and  lingual  surfaces.  In  the  upper  molars  the  central 
inclination  of  the  lingual  surface  is  much  greater  than  that  of 
the  buccal ;  while  in  the  lower  molars  the  central  inclination  of 
the   buccal   surface    is   the   greater.      The   buccal  marginal 

*  In  large  strong  teeth  it  seems  that  the  growth  of  the  dentine  pulp 
is  often  too  great  for  the  enamel  cap,  so  that  the  enamel-forming  cells 
are  drawn  apart,  preventing  a  union  of  the  enamel  plates;  hence  fis- 
sures are  more  frequent  in  large  teeth. 

6 


64  UPPER  FIRST  MOLAR. 


ridge  begins  at  the  mesio-buccal  angle,  in  the  form  of  a  blunt 
cutting  edge,  and  rises  in  a  curved  line  to  the  summit  of  the 
mesio-buccal  cusp  (Fig.  54,  a),  from  which  it  descends  dis- 
tally  to  the  buccal  groove  (i).  From  the  summit  of  this  cusp 
the  mesio-buccal  triangular  ridge  (p)  descends  to  the  mesial 
side  of  the  central  pit  (q).  This  ridge  is  divided  from  the 
mesio  marginal  ridge  by  the  mesio-buccal  supplemental 
groove  (m),  which  is  sometimes  deep,  but  generally  shallow, 
and  occasionally  absent.  From  the  buccal  groove  the  mar- 
ginal ridge  rises  rapidly  to  the  summit  of  the  disto-buccal  cusp 
(b),  then  descends  in  a  curve  to  the  disto-buccal  angle,  to  join 
the  distal  marginal  ridge  (g).  From  the  point  of  this  cusp  the 
disto-buccal  triangular  ridge  (or  triangular  ridge  of  the  disto- 
buccal  cusp,  11),  runs  down  to  the  distal  side  of  the  central  pit, 
where  it  joins  a  ridge  from  the  mesio-lingual  cusp  to  form  the 
oblique  ridge,  or  is  divided  from  this  ridge  by  a  sulcate  dis- 
tal groove. 

72.  The  lingual  marginal  ridge  begins  at  the  mesio- 
lingual  angle  as  a  rounded  edge,  and  rises  in  a  curve  to  the 
summit  of  the  mesio-lingual  cusp  (c),  and  descends,  continu- 
ing its  curve,  into  a  ridge,  meeting  the  triangular  ridge  of  the 
disto-buccal  cusp  to  form  the  oblique  ridge.  However,  in  a 
less  pronounced  form,  this  marginal  ridge  descends  from  the 
summit  of  the  mesio-lingual  cusp  to  the  distal,  where  it  is 
deeply  broken  by  the  disto-lingual  groove.  On  the  distal  side 
of  this  groove  it  rises  abruptly  to  the  summit  of  the  disto-lin- 
gual cusp  (d),  from  which  it  slopes  away  in  a  curve  to  join  the 
distal  marginal  ridge. 

73.  The  mesial  marginal  ridge  (/)  is  a  strong  band  of 
enamel  running  from  the  mesio-buccal  to  the  mesio-lingual 
angle  of  the  occlusal  surface.  It  forms  the  mesial  boundary 
of  the  occlusal  surface,  and  the  angle  of  junction  of  the  mesial 
and  occlusal  surfaces,  or  the  mesio-occlusal  angle.  It  is  low 
in  the  center  of  its  length,  and  rises  toward  both  angles.  It 
is  crossed  near  its  center  by  the  mesial  groove,  usually  as  a 
fine    line,   which   is   often   obliterated   by   wear   early   in   life. 


UPPER  FIRST  MOLAR.  65 


Occasionally  one  or  more  small  tubercles  appear  in  the  central 
portion  of  this  ridge,  inclosed  in  what  seems  to  be  a  division 
of  the  mesial  groove. 

74.  The  distal  marginal  ridge  (g)  is  a  band  of  enamel 
forming  the  distal  boundary  of  the  occlusal  surface,  from  angle 
to  angle,  and  forms  the  angle  of  junction  between  the  occlusal 
and  the  distal  surfaces,  or  the  disto-occlusal  angle.  It  is  low 
in  the  center  of  its  course,  and  is  crossed  by  the  distal  end  of 
the  disto-lingual  groove  as  a  fine  line,  usually  a  little  to  the 
buccal  of  the  central  point. 

75.  The  central  fossa  is  irregularly  circular,  and  is 
formed  by  the  central  inclines  of  the  mesial  marginal  ridge, 
mesio-buccal  cusp,  disto-buccal  cusp,  mesio-lingual  cusp,  and 
oblique  ridge.  It  is  made  irregular,  and  sometimes  angular, 
by  the  depth  of  the  several  sulcate  grooves,  or  by  the  promi- 
nence of  the  triangular  ridges,  especially  that  from  the  mesio- 
buccal  cusp.  The  central  incline  of  the  mesio-lingual  cusp  is 
generally  a  plane  surface,  but  is  sometimes  slightly  concave, 
and  in  about  a  fourth  of  its  examples  there  is  a  low,  triangular 
ridge  running  from  its  apex  directly  to  the  central  pit.  The 
oblique  ridge  is  occasionally  cut  through  by  a  deep  and  wide 
distal  sulcus,  thus  connecting  the  central  with  the  distal  fossa. 
In  a  few  examples  two  supplemental  grooves  or  wrinkles  arise 
from  the  mesial  groove  at  about  the  center  of  its  length,  and 
run,  one  toward  the  mesio-buccal  and  the  other  toward  the 
mesio-lingual  angle  of  the  occlusal  surface.  These  are  often 
of  such  depth  and  width  as  to  form  a  small  supplemental  mesial 
fossa.  Of  these  grooves,  the  mesio-lingual  is  generally  absent, 
and  the  mesio-buccal  (m)  is  generally  present,  though  often 
very  shallow. 

76.  The  distal  fossa  is  formed  by  the  distal  incline  of 
the  disto-buccal  and  mesio-lingual  cusps  and  oblique  ridge, 
which  meet  the  central  incline  of  the  disto-lingual  cusp  and 
distal  marginal  ridge.  It  is  traversed  by  the  disto-lingual 
groove,  which  is  generally  sulcate,  and  deepens  into  a  pit  at 
the  point  where  it  receives  the  distal  groove.    From  the  buccal 


66  UPPER  FIRST   MOLAR. 


portion  a  supplemental  groove,  the  disto-buccal,  runs  well  up 
toward  the  summit  of  the  disto-buccal  cusp,  dividing  its  trian- 
gular ridge  from  the  distal  marginal  ridge. 

yy.  In  some  molars  many  supplemental  grooves  or 
wrinkles  radiate  from  the  centers  of  these  fossae  on  the  inclines 
of  the  ridges  and  cusps,  and  in  some  poorly  developed  teeth 
these  are  deeply  fissured.  The  growth  of  enamel  seems  to 
have  reached  ouf  toward  the  line  of  junction  in  the  form  of 
spiculse,  and  to  have  failed  to  fill  out  the  space. 

78.  The  buccal  surface  of  the  upper  first  molar  (Fig. 
56)  is  irregularly  convex.  Its  length  is  about  equal  to  the 
mesio-distal  breadth  at  the  gingival  line,  while  the  width  at 
the  widest  point,  near  the  occlusal  margin,  is  about  three- 
tenths  greater.  Therefore,  the  mesial  and  distal  margins  con- 
verge toward  the  neck.  The  mesial  margin  is  almost  straight, 
after  the  rounding  of  its  mesio-occlusal  angle,  but  the  distal  is 
convex.  The  occlusal  margin  is  surmounted  by  the  buccal 
cusps  {a,  b),  between  which  there  is  a  deep  notch,  through 
which  the  buccal  groove  passes  from  the  occlusal  to  the  buccal 
surface.  This  groove  passes  centrally  toward  the  gingival  line 
about  half  the  length  of  this  surface,  dividing  the  occlusal  por- 
tion into  a  mesial  and  distal  buccal  ridge.  In  some  examples 
the  groove  continues  across  the  gingival  line  to  the  bifurcation 
of  the  roots.  There  is  a  bucco-gingival  ridge  of  enamel  (e) 
near  the  gingival  line  which  the  buccal  groove  generally  does 
not  cross.  The  mesio-distal  convexity  is  greatest  on  this 
ridge,  and  diminishes  toward  the  occlusal  margin.  The  sum- 
mit of  this  convexity  is  on  the  mesial  half,  in  a  line  with  the 
mesial  root,  and  the  surface  falls  away  rapidly  toward  the 
disto-buccal  angle  of  the  tooth. 

79.  The  lingual  surface  (Fig.  57)  is  divided  in  a  line 
with  the  long  axis  of  the  tooth  into  a  mesial  and  distal  lobe 
by  the  lingual  groove  (i).  Both  lobes  are  smoothly  convex 
from  mesial  to  distal,  and  in  a  less  degree  from  the  gingival 
line  (/)  to  the  occlusal  margin.  The  gingival  line  is  nearly 
horizontal,  and  so  sunken  as  to  give  the  appearance  of  a  gin- 


Fig-  59' 


Fig.  60. 


Fig.  6r. 


Fig.  59*  (Par.  8i). — Right  Upper  First  Molar,  Distal  Surface,  a,  Mesio- 
buccal  cusp;  b,  disto-buccal  cusp;  d,  disto-lingual  cusp;  f,  f,  gingival  line;  k, 
mesial  root;  /,  distal  root;  m,  lingual  root;   0,  concavity  of  the  distal   surface. 

Fig.  60*  (Par.  82). — Left  Upper  First  Molar,  Buccal  Surface.  A  bell- 
crowned  tooth. 

Fig.  61*  (Par.  85). — Upper  First  Molar  showing  the  mesial  and  distal  roots 
united  at  their  apexes. 

Fig.  62*  (Par.  86). — The  Right  Upper  Molars  showing  the  progressive  dimi- 
nution of  the  disto-lingttal  cusp  from  the  first  to  the  third  molar. 


'Illustration,    i5<^    diameters. 


UPPER  FIRST  MOLAR.  69 


gival  enamel  ridge.  The  occlusal  margin  is  surmounted  by 
the  mesio-  and  disto-lingual  cusps  (c,  d),  of  which  the  mesial 
is  usually  the  larger.  In  the  five-cusped  molar  the  fifth  cusp 
{e)  is  seen  on  the  mesio-lingual  lobe.  The  mesial  and  distal 
margins  are  convex,  converging  rapidly  toward  the  lingual 
root.  In  the  few  examples  in  which  the  lingual  groove  is  not 
apparent,  the  lingual  surface  is  smoothly  convex  from  mesial 
to  distal. 

80.  The  mesial  surface  (Fig  58)  is  nearly  flat  in  all 
directions,  and  its  margins  are  rounded  to  the  buccal  and  lin- 
gual surfaces.  Toward  the  occluso-buccal  angle,  the  flat  sur- 
face is  continued  well  up  to  the  occlusal  surface,  which  it  meets 
in  a  fairly  sharp  angle ;  but  as  it  approaches  the  linguo-occlusal 
portion  it  is  progressively  rounded  toward  the  occlusal  surface. 
In  many  molars,  near  the  gingival  line,  half-way  from  buccal  to 
lingual,  this  surface  is  a  little  concave. 

81.  The  distal  surface  (Fig.  59),  in  its  lingual  half,  is 
convex  in  all  directions,  but  in  its  buccal  half  there  is  often 
a  concavity  formed  by  a  considerable  distal  protrusion  of  the 
disto-lingual  lobe.  This  is  a  shallow,  but  marked,  depression 
(0),  running  from  the  bifurcation  of  the  distal  and  the  lingual 
roots  toward  the  disto-buccal  cusp.  It  crosses  the  gingival 
line  at  a  point  about  one-third  distant  from  the  buccal  toward 
the  lingual  margin.  In  many  examples  this  depression  is  more 
central  and  receives  the  distal  termination  of  the  disto-lingual 
groove,  which  may  often  be  traced  as  a  fine  line  nearly  or 
quite  to  the  gingival  border  of  the  enamel.  This  complication 
of  the  surface  makes  the  finishing  of  fillings,  and  the  fitting  of 
bands  for  crowns,  specially  difficult.  This  depression  falls  short 
of  forming  a  concavity  in  about  one-fourth  of  the  first  molars. 

82.  The  root  of  the  upper  first  molar  (Figs.  56  to  61) 
is  divided  into  three  prongs  or  roots* — the  mesial,  or  mesio- 

*  The  divisions  of  the  root  of  a  tooth  are  usually  called  "the  roots," 
and  the  upper  molars  are  said  to  have  three  roots.  The  neck  of  the 
tooth  is,  however,  common  to  all,  and,  more  strictly,  there  is  one  root 
divided  into  several  prongs,  or  fangs.  Some  authors  follow  this  form 
of  expression.  For  instance.  Prof.  Judd  says:  "The  root  of  a  molar 
is  divided  into  three  fangs."  I  see  no  good  reason,  however,  for  not 
calling  them  roots,  the  term  generally  in  use  by  the  dental  profession. 


70  UPPER    SECOND    MOLAR. 

buccal  (k),  the  distal  or  disfo-buccal  (/),  and  the  lingual  (m). 
These  are  usually  quite  widely  separated,  giving  the  tooth  a 
firm  seat  in  its  alveolus.  The  lingual  root  is  the  largest ;  it 
diverges  boldly  to  the  lingual,  and  is  straight,  or  slightly 
curved,  with  the  convexity  to  the  lingual.  It  is  conical,  and 
tapers  regularly  to  an  obtuse  rounded  apex.  In  most  molars 
it  has  a  groove,  a  continuation  of  the  lingual,  on  its  lingual 
side,  running  nearly,  or  quite,  its  whole  length.  In  rare  ex- 
amples this  root  bifurcates. 

83.  The  mesial  root  (k)  is  larger  than  the  distal;  broad 
from  buccal  to  lingual,  and  thin  from  mesial  to  distal,  with 
the  lingual  portion  the  thinner,  and  grooved  on  its  flattened 
sides.  It  diverges  first  to  the  mesial  and  buccal,  and  then 
curves  to  the  distal.  It  tapers  mostly  at  the  expense  of  the 
lingual  thin  edge,  and  ends  in  a  flattened  or  rounded  apex. 

84.  The  distal  root  (/)  is  the  smallest  of  the  three.    It 
--diverges  to  the  distal  and  buccal,  and  is  straight,  or  slightly 

curved,  sometimes  to  the  distal,  sometimes  to  the  mesial,  so 
that  its  apex  approaches  the  mesial  root.  It  is  flattened  on 
its  mesial  and  distal  sides,  but  less  than  the  mesial  root,  and 
tapers  to  a  more  rounded  form,  ending  in  a  slender  point. 

85.  The  roots  of  the  first  molar  are,  perhaps,  more  regu- 
lar in  form  than  those  of  any  other  of  the  molar  teeth ;  but  even 
in  these,  considerable  deviation  from  the  forms  described  will 
occasionally  be  observed  (Figs.  60  and  61). 

UPPER    SECOND    MOLAR. 

86.  The  most  constant  difference  between  the  occlusal 
surfaces  of  the  upper  first  and  second  molars  is  that  the  lat- 
ter tooth  is  smaller,  and  has  an  almost  constant  tendency  to  a 
relatively  smaller  size  of  the  disto-lingual  lobe.|  This  ten- 
dency is  well  seen  in  Fig.  62,  in  which  the  upper  molars  of  a 
very  well  formed  denture  are  drawn  from  the  cast.  This  shows 
the  disto-lingual  lobe  progressively  diminished,  so  that  in  the 
third  molar  it  is  very  small.  When  a  large  number  of  second 
molars  are  examined,  it  is  found  that  the  central  fossse  are  not 


Fig.  64. 


Fig.  65. 


^ 


Fig.  66. 


Fig.  67. 


^FiG.  63*  (Par.   86). — Right   Upper  Second   Molar,   Occlusal  Surface,  with 

three  of  the  cusps  faceted  by  wear.  Tooth  large  and  especially  well  developed,  a, 
Mesio-buccal  cusp;  6,  disto-buccal  cusp;  c,  mesio-lingual  cusp;  d,  disto-lingual 
cusp;  /,  mesial  marginal  ridge;  g,  distal  marginal  ridge;  h,  mesial  groove;  i,  buc- 
cal groo\'e;  /,  distal  groove;  k,  disto-lingual  groove;  /,  distal  fossa;  m,  mesio-buccal 
triangular  groove;  n,  central  pit;  o,  mesio-buccal  triangular  ridge;  p,  disto-buccal 
triangular    ridge;    r,    mesio-lingual    triangular    ridge. 

Fig.  64*  (Par.  86). — Right  Upper  Second  Molar,  Occlusal  Surface,  Tooth 
of  medium  size  and  imperfect  form,  o,  Mesio-buccal  cusp ;  b,  disto-buccal  cusp ;  c, 
mesio-lingual  cusp;  d,  disto-lingual  cusp;  /,  mesial  marginal  ridge;  g,  distal  mar- 
ginal ridge;  h,  mesial  groove;  t,  buccal  groove;  /,  distal  fossa.  The  disto-lingual 
groove  is  imperfect;  tn,  mesio-buccal  triangular  groove;  o,  mesio-buccal  tri- 
angular ridge;  p,  disto-buccal  triangular  ridge,  which  unites  with  the  ridge  from 
the  rriesio-lingual  cusp  to  form  the  oblique  ridge. 

Fig.  65*  (Par.  87). — Right  Upper  Second  Molar  showing  a  form  of  deformity 
peculiar  to  this  tooth  that  is  not  very  common. 

Fig.  66*  (Par.  89).— Right  Upper  Second  Molar  with  the  roots  inclined  to 
the   distal. 

Fig.  67*  (Par.  90).— Right  Upper  Second  Molar,  Distal  Surface,  with  the 
three  roots  compressed  into  one. 

Fig.  68*  (Par.  90). — Right  Upper  Second  Molar,  showing  the  distal  and  lin- 
gual roots  united. 


'Illustration,    ij^^    diameters. 


UPPER  SECOND   MOLAR.  73 

SO  regularly  formed  as  in  the  first,  being  often  small,  even  in 
large,  well-developed  teeth  (Fig.  63),  and  the  cusps  compara- 
tively low,  with  a  relatively  greater  inclination  of  the  lingual 
surface  toward  the  summit  of  the  mesio-lingual  cusp.  In 
many  examples  the  distal  fossa  is  reduced  to  a  mere  pit  (Fig. 
64),  and  the  lingual  marginal  ridge  is  continued  from  the  sum- 
mit of  the  mesio-lingual  cusp  distally  to  the  disto-lingual  angle, 
where  it  joins  the  distal  marginal  ridge,  as  in  Fig.  64,  making 
practically  a  three-cusped  tooth.  In  many  of  these,  after  the 
tooth  is  a  little  worn,  the  disto-lingual  groove  cannot  be  traced 
across  the  lingual  marginal  ridge,  nor  on  the  lingual  surface; 
but  a  fine  line  is  generally  seen  crossing  the  distal  marginal 
ridge. 

87.  The  upper  second  molar  is  Hable  to  a  peculiar 
deformity,  which  I  have  not  seen  in  any  other  tooth.  The 
crown  is  greatly  flattened  from  mesial  to  distal,  occasionally 
to  such  an  extent  as  to  present  none  of  its  usual  lines.  In 
the  extreme  cases  (Fig.  65)  there  is  one  central,  long-shaped 
sulcus  running  from  buccal  to  lingual,  formed  by  the  central 
inclines  of  a  ridge  encircling  the  occlusal  surface.  This  ridge 
may  be  broken  at  intervals  by  shallow  grooves  crossing  it. 
Usually,  much  of  the  central  inclination  of  this  ridge  is  wrin- 
kled, and  often  there  are  many  small  fissures.  The  mesial  sur- 
face is  commonl}^  deeply  concave,  and  the  distal  convex. 

88.  In  well-developed  second  molars,  the  form  of  the 
buccal,  lingual,  mesial,  and  distal  surfaces  is  much  the 
same  as  in  the  first  molar,  though  rather  more  convex,  and 
concavities  in  the  mesial  and  distal  surfaces  are  not  so  frequent. 
However,  in  teeth  with  large  disto-lingual  cusps,  the  concavity 
of  the  distal  surface  is  about  the  same  as  in  the  first  molar  (Par. 
81).  The  lingual  groove  is  generally  not  sulcate,  though  it  is 
usually  seen  as  a  fine  line  in  unworn  teeth.  It  is  often  near  the 
disto-lingual  angle,  and,  when  sulcate,  it  generally  disappears 
by  becoming  shallower  about  half-way  toward  the  gingival 
line ;  rarely  it  runs  across  the  gingival  line,  and  in  that  case  the 
lingual  root  is  grooved,  as  in  the  first  molars. 


74  UPPER    THIRD    MOLAR. 

89.  The  neck  of  the  tooth  is  less  regular  in  its  outline 
than  in  the  first  molar.  In  the  average,  it  is  more  flattened 
from  mesial  to  distal,  and  on  lines  that  converge  more  to  the 
lingual.  On  the  buccal  surface,  the  mesio-buccal  ridge  is 
relatively  more  prominent,  and  at  the  neck  the  surface  slopes 
away  more  toward  the  distal,  so  that  in  many  examiples,  the 
distal  roof  seems  compressed  between  the  mesial  and  lingual 
roots. 

90.  The  roots  of  this  tooth  are  the  same  in  number  and 
general  form  as  in  the  first  molar,  but  they  spread  less,  and 
are  curved  more  to  the  distal /(Fig.  66).  There  is  also  much 
more  variety  of  the  comparative  size  of  the  root  and  crown 
than  in  the  first  molar.  In  many  the  root  is  single,  with  the 
outlines  of  the  division  marked  by  grooves  of  variable  depth 
(Fig.  67)  ;  or  two  of  the  roots  may  be  connected,  while  the  third 
is  free.  Sometimes  this  union  is  the  lingual  with  the  distal 
(Fig.  68)  ;  but  oftener  it  is  the  lingual  with  the  mesial  root. 

UPPER  THIRD  MOLAR. 

91.  The  upper  third  molar  deviates  from  the  typical  form 
of  the  first  more  than  does  the  second.  Yet,  in  dentures  of  the 
best  form,  it  presents  the  same  developmental  lines,  fossse, 
and  cusps  (Fig.  69).  The  disto-lingual  lobe  is  very  much 
smaller,  and  in  many  examples  is  entirely  wanting.  /  Of  the 
examples  in  my  possession,  about  twenty-one  per  cent,  show  a 
diminutive  disto-lingual  cusp ;  thirty-two  per  cent,  show  a  pit 
in  the  position  of  the  distal  fossa,  and  some  portion  of  the  disto- 
lingual  groove,  but  no  depressed  groove  over  the  lingual  mar- 
ginal ridge;  it  is  similar  to  that  shown  in  Fig.  64.  The  re- 
mainder, or  about  forty-seven  per  cent.,  have  no  disto-lingual 
lobe.  Of  the  latter,  three-fourths  are  properly  three-cusped 
teeth  in  which  the  oblique  ridge  becomes  the  distal  marginal 
ridge,  and  the  distal  groove  runs  over  to  the  distal  surface  (Fig. 
70).  In  the  remainder,  there  is  only  an  irregular  ridge  (Fig. 
71),  forming  a  central  fossa,  so  marked  with  wrinkles  or  sup- 
plemental grooves  that  the  developmental  lines  are  not  satis- 


o^_£_L^ 


Fig.  71. 


Fig. 


Fig.  73- 


^^—'9tg.  69*  (Par.  91). — Right  Upper  Third  Molar,  Occlusal  Surface,  of  typical 
form,  a,  Mesio-buccal  cusp;  b,  disto-buccal  cusp;  c,  mesio-lingual  cusp;  d,  disto- 
lingual  cusp;  e,  mesial  marginal  ridge;  /,  distal  marginal  ridge;  g,  mesio-buccal 
triangular  ridge;  h,  disto-buccal  triangular  ridge;  i,  mesial  groove;  k,  buccal 
groove;  /,  distal  groove;  m,  disto-lingual  groove;  n,  central  pit;  0,  mesio-buccal 
triangular  groove. 

Fig.  70*  (Par.  91). — Right  Upper  Third  Molar,  Occlusal  Surface,  three 
cusped,  a,  Mesio-buccal  cusp;  b,  disto-bticcal  cusp;  c,  lingual  cusp;  e,  mesial  mar- 
ginal ridge;  h,  distal  marginal  ridge;  /,  mesial  groove;  k,  buccal  groove;  /,  distal 
groove;   0,   mesio-buccal   triangular  groove. 

Fig.  71*  (Par.  91). — Right  Upper  Third  Molar,  Occlusal  Surface.  Young, 
unworn  tooth  of  imperfect  form,  a,  Mesio-buccal  cusp;  b,  disto-buccal  cusp;  c,  lin- 
gual cusp;  e,  mesial  marginal  ridge;  /,  distal  marginal  ridge;  g,  mesial  groove;  h, 
buccal  groove;  i,  distal  groove.  Several  supplemental  grooves  are  seen  radiating 
from  the  central  pit. 

Fig.  72*  (Par.  94). — Right  Upper  Third  Molar,  Buccal  Surface.  The  roots 
are  not  quite  complete,  and  show  the  funnel-shaped  openings  at  the  apex. 

Fig.  73*  (Par.  94). — Left  Upper  Third  Molar  with  five  roots. 


'Illustration,   1J-2  diameters. 


UPPER    THIRD    MOLAR.  77 

factorily  made  out.     Many  examples  of  the  three-cusped  teeth 
show  much  relative  diminution  of  the  disto-buccal  lobe. 

92.  The  upper  third  molar  is  the  smallest  of  the  mo- 
lars,* and  is  more  irregular  in  its  size  and  conformation  than 
the  first  or  second  molar.  On  account  of  the  small  size  of 
the  disto-lingual  lobe,  the  distal  portion  of  the  tooth  is  much 

s smailerutlian  .  th£_  mesi^     [and   in   the   three-cusped   teeth   the 

crown  becomes  triangular,  with  its  angles  well  rounded.     (Fig. 
70.) 

93.  The  mesial  surface  resembles  that  in  the  upper 
first  and  second  molars,  but  is  more  rounded,  so  that  a  con- 
cave portion  is  less  frequent,  and  the  distal  surface  is  well 
rounded.  The  lingual  and  buccal  surfaces  are  more 
rounded  than  the  same  surfaces  in  the  other  upper  molars. 
The  gingival  line  is  usually  horizontal  in  its  course  around  the 
neck  of  the  tooth,  except  that,  in  a  few  examples,  there  is  a 
slight   curvature  on  the  mesial   surface.      Many   upper  third 

_  molars  are  much  flattened  from  mesial  to  distal.  These  gener- 
ally have  a  considerable  concavity  on  the  mesial  surface.  Oc- 
casionally teeth  are  found  that  are  also  abnormally  small  and 
have  the  appearance  of  supernumeraries.  More  rarely  this 
tooth  fails  to  develop,  and  is  wanting  entirely, 

94.  The  root  of  the  upper  third  molar  has,  in  the  more 
regular  forms,  the  three  divisions  common  to  the  upper  mo- 
lars, though  relatively  smaller  and  not  so  widely  separated  as 
those  of  the  first  and  second  molars ;  and  often  end  in  slender 
conical  points;  many  have  but  a  single  root;  but  in  most  of 
these  the  three  roots  are  outlined  by  grooves  of  more  or  less 
depth.  A  considerable  number  have  more  than  three  roots, 
which  are  irregular  in  size  or  form  (Fig.  73).  Four,  five,  six, 
and  even  seven  or  eight  divisions  are  sometimes  met.  The 
neck  is  then  generally  broad  from  buccal  to  lingual,  and  the 

„,^ occlusal  surface  of  the  crown  irregularly  formed.  /  Many  of  the 

three-cusped  teetli  have  the  root  without  divisions. 

*  Forty  upper  first  molars  balanced  sixty  upper  third  molars. 


78  THE  LOWER  MOLARS THE  LOWER   FIRST   MOLAR. 


THE  LOWER  MOLARS. 

95.  The  lower  molars  differ  so  much  from  each  other, 
especially  the  first  and  second,  that  each  must  be  separately 
described. 

THE  LOWER  FIRST  MOLAR. 

96.  The  lower  first  molar  is  the  sixth  tooth  from  the 
median  line  in  the  lower  jaw.  It  proximates  the  lower  second 
bicuspid  with  its  mesial  surface,  and  the  lower  second  molar 
with  its  distal.  Next  to  the  upper  first  molar,  it  is  the  largest 
tooth  in  the  denture.*  The  outline  of  the  occlusal  surface 
(Figs.  74  and  75),  when  seen  in  a  line  with  the  long  axis  of  the 
■tooth,  is  trapezoidal,  with  the  buccal  marginal  line  the  longest,  _ 
The  buccal  angles  are  about  equally  acute,  while  the  lingual 
angles  are  equally  obtuse,  and  all  are  more  or  less  rounded. 
The  buccal  margin  is  convex,  but  made  irregular  by  two  buc- 
cal grooves.  The  lingual  margin  is  nearly  straight,  but  some- 
times slightly  concave,  or  notched  in  the  center  of  its  length, 
by  the  lingual  groove ;  but  more  generally  it  is  slightly  convex. 
The  mesial  and  the  distal  margins  are  nearly  straight  in  the 
best  formed  teeth ;  though  the  distal  is  sometimes  considerably 
convex,  as  the  fifth,  or  disto-lingual  cusp  is  more  or  less  promi- 
nent. All  of  these  margins  vary  as  to  their  convexity ;  the  rule 
being  that,  in  teeth  of  large  size  and  symmetrical  development, 
they  approach  nearer  to  straight  lines. 

97.  Each  of  these  marginal  portions  is  surmounted  by 
the  mesial,  buccal,  lingual,  and  distal  marginal  ridges,  which 
form  a  continuous  elevation  of  irregular  height  around  the 
margins  of  the  occlusal  surface,  and  on  which  there  are  five 
cusps.  The  central  inclinations  of  these  ridges  form  the 
central  fossa.  On  the  mesial,  lingual,  and  distal,  the  sum- 
mits of  these  ridges  are  close  on  the  margins  of  the  surface; 
but  on  the  buccal,  there  is  an  inclination  of  the  buccal  surface ; 
that  carries  the  summit  of  the  ridge  considerably  toward  the 
central  axis  of  the  tooth. 

*  Forty-two  upper  first  molars  balanced  forty-six  lower  first  molars. 


Fig.  76. 


Fig.  77- 


Fig.  74*  (Par.  96).— Left  Lower  First  Molar,  Occlusal  Surface,  of  typical 
form,  a,  Mesio-buccal  ctisp;  h,  disto-buccal  cusp;  c,  mesio-lingual  cusp;  d,  disto- 
lingual  cusp;  e,  distal  cusp;  f,  mesial  marginal  ridge;  g,  distal  marginal  ridge;  h, 
mesio-bticcal  triangular  ridge;  i,  disto-buccal  triangular  ridge;  k,  disto-Iingual  tri- 
angular ridge;  /,  mesio-lingual  triangular  ridge;  m,  distal  triangular  ridge;  ;;, 
mesial  groove;  0,  buccal  groove;  p,  disto-buccal  groove;  r,  distal  groove;  s,  lingual 
groove. 

Fig.  7S*  (Par.  96).— Right  Lower  First  Molar,  Occlusal  Surface,  a, 
Mesio-buccal  cusp;  b,  disto-buccal  cusp;  c,  mesio-lingual  cusp;  d,  disto-lingual 
cusp;  e,  distal  cusp;  f,  mesial  marginal  ridge;  g,  distal  marginal  ridge;  h,  mesial 
triangular  ridge;  i,  disto-buccal  triangular  ridge;  k,  mesio-lingual  triangular  ridge; 
/,  disto-lingual  triangular  ridge;  ;;,  mesial  groove;  0,  buccal  groove;  p,  disto-buccal 
groove;  r,   distal  groove;   s,  lingual  groove;    t,  mesio-buccal   triangular   groove. 

Pig.  76*  (Par.  i04).^LErT  Lower  First  Molar,  Buccal  Surface,  a,  ]Mesio- 
buccal  cusp;  b,  disto-buccal  cusp;  c,  distal  cusp;  d,  bucco-gingival  ridge;  e,  buccal 
pit,  /,  gingival  line;  ^,  mesial  root ;  /;,  distal  root;  /,  buccal  groove;  k,  disto-buccal 
groove. 

Fig.  yy*  (Par.  104). — Left  Lower  First  Molar,  Buccal  Surface,  with 
prominent    cusps.      Reference  the   same   as   for   Fig.   76. 


*IIlustration,    i>^    diameters. 
7 


THE    LOWER    FIRST    MOLAR.  8 1 

98.  The  occlusal  surface  has  five  developmental 
grooves  (Figs.  74  and  75) — the  mesial,  buccal,  disto-buccal, 
lingual,  and  distal — which  divide  it  into  five  developmental 
parts,  or  lobes.  These  are  the  mesio-buccal  (a),  disto-buccal 
(b),  mesio-lingual  (c),  disto-lingual  (d),  and  distal  (^) lobes; 
each  bearing  a  cusp  of  the  same  name.  ^The  mesial  groove 
~Xn)' runs  from  the  central  fossa  over  the  mesial  marginal  ridge 
to  the  mesial  surface.  On  the  mesial  marginal  ridge  it  is  usu- 
ally a  fine  line  which  is  soon  obliterated  by  wear.  Occasion- 
ally, this  is  divided  into  two  branches,  with  a  small  tubercle  on 
the  mesial  marginal  ridge  between  them  (Fig.  74,  /).  In  many 
examples  there  is  a  supplemental  groove  which  rises  from  the 
mesial  groove  at  about  the  center  of  its  length,  and  runs  toward 
the  mesio-buccal  angle.  This  is  the  mesio-buccal  triangular 
groove  (Fig.  75,  i^).  It  divides  the  mesial  marginal  ridge  from 
the  triangular  ridge  of  the  mesio-buccal  cusp.  More  rarely 
there  is  also  a  similar  groove  running  toward  the  mesio-lingual 
cusp.  When  these  are  deep,  they  form  a  mesial  supplemental 
fossa  (Fig.  75,  t).  The  buccal  groove  (0)  runs  in  a  deep 
sulcus  from  the  central  pit  to,  and  over,  the  buccal  marginal 
ridge  to  the  buccal  surface,  and  divides  the  mesio-buccal  from 
the  disto-buccal  cusp.  The  disto-buccal  groove  (p)  also 
runs  bucco-distally  from  the  central  pit  over  the  buccal  ridge, 
more  or  less  near  the  distal  angle,  as  the  distal  cusp  is  large  or 
small.  It  divides  the  disto-buccal  lobe  from  the  distal.  The 
lingual  groove  (s)  runs  from  the  central  pit  in  a  deep  sulcus 
to,  and  over,  the  lingual  marginal  ridge  onto  the  lingual  sur- 
face, and  divides  the  two  lingual  lobes.  The  distal  groove 
(r)  runs  distally  over  the  distal  marginal  ridge,  and  divides  the 
disto-lingual  lobe  from  the  distal.  Frequently  this  groove  can 
be  traced  some  distance  toward  the  gingival  line  on  the  distal 
surface.  The  mesial  and  distal  grooves  form  a  line  traversing 
the  whole  extent  of  the  occlusal  surface,  from  mesial  to  distal, 
in  the  center  of  which  a  V-shaped  deflection  is  formed  with  its 
point  to  the  lingual,  the  base  receiving  the  point  of  the  triangu- 
lar ridge  (i)  of  the  disto-buccal  cusp. 


82  THE    LOWER    FIRST    MOLAR. 

99.  In  most  examples  the  central  fossa  occupies  all 
the  occlusal  surface  within  the  circle  of  the  summit  of  the  mar- 
ginal ridges,  though,  occasionally,  one  or  more  supplemental 
fossae  are  divided  from  it  by  high  triangular  ridges  running 
down  from  the  cusps  (Fig.  75,  h,  k).  The  surface  of  the  fossa 
is  made  irregular  in  most  of  these  teeth  by  deep  sulci  on  the 
lines  of  the  grooves,  separating  the  cusps  and  triangular  ridges. 

100.  The  occlusal  surface  of  the  lower  first  molar  has 
five  cusps,  one  on  each  side  of  the  five  lobes  or  three  on  the 
buccal  marginal,  and  two  on  the  lingual  marginal  ridge.* 
These  cusps  are  formed  by  the  grooves  previously  described 
(Par.  98),  which  pass  over  the  ridges  in  depressions  of  variable 
depth,  thus  subdividing  the  crests  of  the  ridges  into  obtuse  ele- 
vations. Usually,  these  are  not  so  high  and  prominent  as  the 
cusps  of  the  upper  molars.  The  mesio-buccal  (Figs.  74  and 
75,  a)  is  the  largest  and  strongest  of  the  buccal  cusps,  and  oc- 
cupies rather  more  than  one-third  of  the  buccal  marginal  ridge. 
From  its  crest  a  triangular  ridge  {h)  runs  down  centrally  to  the 
junction  of  the  mesial  and  buccal  grooves,  and  is  divided  from 
a  similar  triangular  ridge  from  the  mesio-lingual  cusp,  by  the 
mesial  groove.  When  these  two  ridges  are  high,  they  form,  in 
conjunction  with  triangular  grooves  between  them  and  the 
mesio-marginal  ridge,  a  mesial  supplemental  fossa.  The  disto- 
buccal  cusp  {b)  is  of  less  extent  from  mesial  to  distal,  but  has 
a  longer  triangular  ridge,  though  not  so  high,  which  ends  in 
the  point  of  the  V-shaped  deflection  of  the  mesial  and  distal 
grooves,  or  at  their  junction. 

loi.  The  lingual  cusps  {c,  d)  are  about  equal  in  size 
and  height  (perhaps  the  mesial  is  a  little  the  higher  on  the 
average).  They  have  strong  triangular  ridges  {k,  I)  which 
terminate  in  the  angles  formed  by  the  junction  of  the  lingual 
groove  with  the  mesial  and  distal  grooves  in  the  central  pit. 

102.  The  distal  cusp  {e)  occupies  the  distal  portion  of 
the   buccal    ridge,   and    forms   the    disto-buccal   angle   of   the 

*  In  some  rare  cases  lower  first  molars  have  but  four  cusps,  and 
then  the  tooth  is  like  the  lower  second  molar.     (Pars.  109,  no.) 


THE    LOWER    FIRST    MOLAR.  83 

occlusal  surface.!  It  is  the  distinguishing  mark  of  the  lower 
first  molar,  being  but  very  rarely  absent  in  that  tooth,  and 
never  present  in  the  lower  second  molar.  It  is  the  smallest 
of  the  five  cusps,  and  varies  most  in  its^  relative  size.  1  In  some 
examples  it  is  almost  or  quite  as  large  as  the  ciisto-buccal 
cusp.  In  others,  especially  in  small  and  poorly  developed 
teeth,  it  may  be  reduced  to  a  mere  tubercle,  occupying  the 
buccal  portion  of  the  distal  marginal  ridge  and  the  immediate 
disto-buccal  angle.  The  central  incline  of  this  cusp  is  com- 
monly nearly  flat,  but  occasionally  has  a  rounded  crest.  It 
ends  in  a  point  at  the  junction  of  the  distal  and  disto-buccal 
grooves. 

103.  In  this  tooth  there  is  often  a  deep  pit  at  the  junc- 
tion of  the  mesial,  distal,  and  lingual  grooves.  Less  fre- 
quently there  is  also  a  pit  at  the  junction  of  the  mesial  and 
buccal  grooves,  and  at  the  junction  of  the  distal  and  disto- 
buccal  grooves.  The  grooves  are  often  fissured  for  a  short 
distance  from  the  pits,  especially  in  the  deeply  sulcate  lingual 
groove.  In  some  very  poorly  developed  teeth  fissures  may 
be  found  in  any  part  of  the  grooves. 

104.  The  buccal  surface  of  the  lower  first  molar  (Figs. 
76  and  ']'/^,  when  seen  at  right  angles  with  the  long  axis  of  the 
tooth,  is  irregularly  trapezoidal  in  form,  with  the  occlusal 
margin  about  two-sevenths-  longer  than  the  gingival.  The 
mesial  and  distal  margins  converge  toward  the  gingival,  and 
the  angles  with  the  occlusal  surface  are  about  equally  acute. 
The  occlusal  margin  is  broken  into  three  elevations,  or  cusps, 
by  the  buccal  and  disto-buccal  grooves.  The  gingival  line  is 
straight,  or  slightly  curved,  with  the  concavity  toward  the 
occlusal  surface.  The  mesial  and  the  distal  lines  are  slightly 
convex.  The  buccal  surface  is  convex  in  all  directions ;  but 
the  line  of  convexity  from  mesial  to  distal  is  broken  toward 
the  occlusal  margin  by  the  buccal  and  disto-buccal  grooves, 
which  pass  over  from  the  occlusal  surface^^The  buccal 
groove  (i)  is  usually  a  little  to  the  mesial  of  the  central  line 
of  the  surface,  and  often  ends  in  a  deep  pit  ((?),  about  half-way 


84  THE    LOWER    FIRST    MOLAR. 

from  the  occlusal  to  the  gingival  margin.  Exceptionally,  this 
groove  is  continued  to  the  bifurcation  of  the  root.  /  The  disto- 
buccal  groove  (k)  is  near  the  disto-buccal  angle,  and  its 
course  is  toward  the  gingival  line,  with  a  distal  inclination. 
It  is  usually  lost  to  sight  by  becoming  shallower,  but  in  some 
examples  it  may  be  traced  to  the  gingival  line.  The  enamel 
terminates  in  a  marked  inclination  toward  the  gingival  line, 
fonning  the  bucco-gingival  ridge. 

105.  The  lingual  surface  of  this  tooth  (Figs.  78  and  79) 
is  slightly  convex  in  all  directions.  It  forms  a  fairly  sharp 
angle  with  the  occlusal  surface,  but  is  rounded  away  toward 
the  mesial  and  distal  surfaces.  On  account  of  the  lingual 
convergence  of  the  mesial  and  distal  surfaces,  the  lingual 
surface  is  much  shorter  mesio-distally  than  the  buccal.  The 
occlusal  margin  is  deeply  notched  by  the  passage  of  the  lingual 
groove  (i),  which  usually  terminates  near  the  center  of  the 
surface  by  becoming  shallower. 

106.  The  mesial  surface  (Fig.  80)  is  very  irregular  in 
outline,  and  often  the  occlusal  margin  is  deeply  concave. 
The  gingival  curvature  is  generally  marked,  and  the  buccal 
and  lingual  marginal  lines  convex.  The  buccal  margin  of 
this  surface  is  more  convex  than  the  lingual,  and  its  curva- 
ture is  at  such  an  incline  as  to  render  the  gingival  marginal 
line  much  longer  than  the  occlusal.  The  surface  is  slightly 
convex,  though  almost  flat ;  but,  in  the  central  portion,  near 
the  gingival  line,  it  is  sometimes  slightly  concave  from  buccal 
to  lingual.  It  is  rounded  away  toward  the  mesio-buccal  and 
mesio-lingual  angles.  With  the  occlusal  surface  it  forms  a 
sharp  angle  in  the  central  portion,  but  this  is  rounded  in  its 
buccal  and  lingual  portions.  In  the  direction  of  the  long 
axis  of  the  tooth,  there  is  usually  a  concavity  at  the  junction 
of  the  enamel  and  cementum. 

107.  The  distal  surface  (Fig.  81)  is  smoothly  convex 
from  buccal  to  lingual.  From  the  occlusal  surface  to  the 
gingival  line  it  is  straight  or  slightly  convex,  but  forms  a 
considerable  concavity  at  the  junction  of  the  crown  with  the 


Fig.  78. 


Fig.  79. 


Fig.  80. 


Fig.  82. 


Fig.  78*  (Par.  105). — Left  Lower  First  Molar,  Lingual  Surface,  a,  Mesio- 
buccal  cusp;  b,  disto-buccal  cusp;  c,  distal  cusp;  d,  mesio-Iingual  cusp;  e,  disto- 
lingual  cusp;  /,  /,  gingival  line;  g,  mesial  root;  h,  distal  root;  the  roots  are 
spread  wide  apart;  i,  lingual  groove. 

Fig.  79*  (Par.  105). — Left  Lower  First  Molar,  Lingual  Surface.  This  tooth 
has  prominent  cusps,  and  the  roots  are  straight  and  close  together.  References  the 
same  as  for  Fig.  78. 

Fig.  80*  (Par.  106). — Left  Lower  First  Molar,  Mesial  Surface,  c,  Mesio- 
buccal  cusp;  d,  mesio-lingual  cusp;  e,  mesial  surface,  point  of  concavity;  /,  f, 
gingival   line ;  g,  mesial  root   with   broad   groove. 

Fig.  81*  (PsiY.  107). — Left  Lower  First  Molar,  Distal  Surface.  The  cusps 
are  very  prominent,  a,  Mesio-buccal  cusp;  b,  disto-buccal  cusp;  c,  distal  cusp;  d, 
mesio-lingual  cusp;  e,  disto-lingual  cusp;  /,  gingival  line;  g,  mesial  root;  h,  distal 
root. 

Fig.   82*   (Par.    108). — Lower   First   Molar,   with  three  roots. 


*IIlustration,    ij^    diameters. 


THE    LOWER    SECOND    MOLAR.  S? 

root,  which  occasionally  forms  a  sharp  angle,  but  generally 
is  well  rounded.  The  occlusal  margin  is  often  deeply  notched 
by  the  distal  groove.  In  a  few  examples  the  disto-buccal 
groove  is  deep  after  passing  over  the  marginal  ridge,  and  in 
its  distal  inclination  forms  a  slight  concavity  near  the  disto- 
buccal  angle. 

io8.  The  root  of  the  lower  first  molar  is  divided  into 
two  prongs  (Figs.  76  to  82),  and  this  division  is  usually  close 
to  the  crown,  closer  than  in  any  other  tooth  in  the  mouth. 
The  mesial  root  (g)  inclines  first  to  the  mesial,  and  then 
curves  regularly  toward  the  distal.  It  is  broad  from  buccal 
to  lingual,  and  is  much  thinned  from  mesial  to  distal,  so  that 
ift~er0s«-"seetions  it  measures  double  as  much  one  way  as  the 
other,  yit  is  usually  slightly  concave  on  both  mesial  and  distal 
surfaces,  and  tapers  regularly,  but  not  rapidly,  from  the  bifur- 
cation to  the  apex,  and  ends  in  a  flattened  but  well-rounded 
point.  The  distal  root  (h)  inclines  to  the  distal  at  first,  and 
afterward  is  nearly  or  quite  straight.  In  some  examples  the 
apical  half  curves  to  the  distal,  but  more  often  toward  the 
mesial,  so  that  the  apexes  of  the  two  roots  are  inclined  toward 
each  other.  It  is  narrower  from  buccal  to  lingual  than  the 
mesial  root,  and  more  nearly  round,  being  but  rarely  concave 
or  grooved  on  either  mesial  or  distal  surface.  It  tapers  quite 
regularly,  and  more  nearly  to  a  point  than  the  mesial  root, 
though  the  apex  is  generally  well  rounded.  The  form  of  the 
root  is  regular,  rarely  deviating  much  from  its  type.  Occa- 
sionally, however,  the  division  of  the  root  is  incomplete.  |  The 
mesial  root  is  occasionally  divided,  giving  the  tooth  three 
roots  (Fig.  82)  ;  and  I  have  seen  a  few  in  which  the  distal  root 
was  divided  also,  giving  four  roots. 

THE    LOWER    SECOND    MOLAR. 

109.  The  most  characteristic  difference  between  the 
lower  first  and  second  molars  is  the  absence  of  the  fifth  lobe 
in  the  second,*  and  the  general  change  of  form  which  this 
absence  implies ;  the  other  parts  of  the  tooth  being  similar. 

*  Since  the  publication  of  the  third  edition  of  this  work  three  cases 
have  been  reported  to  me,  two  of  which  were  accompanied  by  plaster 
casts  in  which  di^al  lobes  with  cusps  were  observed  upon  the  lower 
second  molars.  In  all  of  them  the  cusps  were  small,  though  fairly 
well  formed.    These  are  certainly  very  rare  cases. 


THE    LOWER    SECOND    MOLAR. 


iio.  When  the  occlusal  surface  is  seen  in  a  Hne  with 
the  long  axis  of  the  tooth  (Fig.  83),  the  outline  of  the  crown 
is  nearly  a  parallelogram,  with  angles  rounded  and  the  lines 
slightly  convex,  the  buccal  most.  The  summits  of  the  mar- 
ginal ridges  are  close  to  the  mesial,  distal,  and  lingual  mar- 
gins, while  the  buccal  is  carried  over  toward  the  lingual  by 
the  inclination  of  the  buccal  surface.  The  central  inclines  of 
the  marginal  ridges  form  a  deep  central  fossa,  in  the  center 
of  which  there  is  usually  a  deep  pit. 

111,  There  are  four  developmental  grooves,  all  aris- 
ing from  the  central  pit.  The  mesial  groove  (/)  runs  to  the 
mesial  margin  and  crosses  the  mesial  marginal  ridge  as  a  fine 
line,  which  is  often  obliterated  by  wear.  The  distal  groove 
(0)  runs  in  a  similar  way  to  the  distal  surface.  These  two 
grooves  divide  the  occlusal  surface  from  mesial  to  distal,  and 
centrally,  between  the  summits  of  the  buccal  and  lingual 
marginal  ridges.  The  buccal  groove  (m)  runs  from  the  cen- 
tral pit  to  the  buccal  margin,  and  over  it  to  the  buccal  surface, 
dividing  the  buccal  ridge  into  two  buccal  cusps,  while  the 
lingual  groove  (n)  runs  to  and  over  the  lingual  marginal 
ridge,  dividing  it  also  into  two  lingual  cusps.  The  two  divide 
the  tooth  from  buccal  to  lingual,  into  nearly  equal  parts.  The 
mesial  portion  is  usually  slightly  the  larger.  The  four  grooves 
form  a  cross  through  the  occlusal  surface,  dividing  it  into 
four  lobes,  or  developmental  parts,  on  each  of  which  there 
is   a   cusp   and   a  triangular  ridge,  j  In  some   examples   the 

"grooveT^do^nor  exactly  meet  at  the  central  pit.  The  lingual 
may  rise  to  the  mesial  of  the  buccal,  or  vice  versa;  or,  a  similar 
variation  may  occur  in  the  central  ends  of  the  mesial  and  distal, 
causing  irregularity  of  the  contour  of  the  central  fossa.  Occa- 
sionally, the  lobes  are  of  unequal  size,  or  the  cusps  are 
unequally  developed,  giving  rise  to  imperfect  forms  (Fig.  84). 

112.  On  the  average,  the  cusps  of  the  lower  second 
molar  are  higher  and  more  pointed,  and  the  triangular  ridges 
are  more  prominent  than  in  the  first  molar.     The  mesio-buccal 


Fig.  87. 


Fig-.  86. 


Fig.  89. 


/Sr— 


Fig.  83*  (Par.  iio).^Right  Lower  Second  Molar,  Occlusal  Surface,  of 
typical  form,  a,  Mesio-buccal  cusp;  b,  disto-buccal  cusp;  c,  mesio-lingual  cusp;  rf, 
disto-lingual  cusp;  e,  mesial  marginal  ridge;  /,  distal  marginal  ridge;  g,  mesio- 
buccal  triangular  ridge;  h,  disto-buccal  triangular  ridge;  /,  mesio-lingual  triangular 
ridge;  k,  disto-lingual  triangular  ridge;  /,  mesial  groove;  m,  buccal  groove;  n, 
lingual  groove;   0,  distal  groove. 

Fig.  84*  (Par.  113). — Right  Lower  Second  Molar,  Occlusal  Surface,  of  im- 
perfect form,  a,  Mesio-buccal  cusp;  b,  disto-buccal  cusp;  c,  mesio-lingual  cusp;  li, 
disto-lingual  cusp;  e,  mesial  marginal  ridge;  f,  distal  rnarginal  ridge;  g,_  mesio- 
buccal  triangular  ridge;  h,  disto-buccal  triangular  ridge;  i,  mesio-lingual  triangular 
ridge;  k,  disto-lingual  triangular  ridge;  /,  mesial  groove;  m,  buccal  groove;  n, 
lingual    groove;    0,    distal    groove. 

Fig.  85*  (Par.  115). — Left  Lower  Second  Molar,  Buccal  Surface,  a,  Mesio- 
buccal  cusp;  b,  disto-buccal  cusp;  c,  buccal  groove;  d,  buccal  pit;  /,  gingival  line; 
g,   mesial  root;   h,   distal  root. 

Fig.  86*  (Par.  116). — Left  Lower  Second  Molar,  Lingual  Surface,  a, 
Mesio-buccal  cusp;  b,  disto-buccal  cusp;  c.  mesio-lingual  cusp;  d,  disto-lingual 
cusp-;    e,   lingual    groove;    /,    gingival   line;    c,    mesial    root;    h,    distal    root. 

Fig.  87*  (Par.  117). — Left  Lower  Second  Molar,  Mesial  Surface,  a,  Mesio- 
buccal  cusp;  c,  mesio-lingual-cusp;  d,  point  of  proximal  contact  of  mesial  surface; 
/,   gingival  line;  g,  mesial  root. 

Fig.  88*  (Par.  118). — Left  Lower  Second  Molar,  Distal  Surface,  a,  Mesio- 
buccal  cusp;  h,  disto-buccal  cusp;  c,  mesio-lingual  cusp;  d,  disto-lingual  cusp;  e, 
point  of  proximate  contact  of  the  distal  surface;  /,  gingival  line;  h,  distal  root. 

Fig.  89*  (Par.  ii9).^Right  Lower  Second  Molar,  Lingual  Surface.  The 
roots   are   curved   very   much   to   the   distal. 

•Illustration,   iJ/<   diameters. 


THE   LOWER   SECOND    MOLAR.  QI 

^  and  mesio-lingual  cusps  are  generally  a  little  larger  than  the 
disto-buccal  and  disto-lingual ;  also,  the  mesio-buccal  and 
mesio-lingual  triangular  ridges  (Fig.  83,  g,  i)  are  usually  more 
prominent.  The  crests  of  these  ridges  do  not  run  directly 
toward  the  central  pit,  but  the  two  mesial  ones  meet  mesially 
of  the  central  pit,  while  the  two  distal  meet  distally  of  it. 
When  they  are  high,  they  form  transverse  ridges  by  their 
junction,  which  separate  a  mesial  and  a  distal  supplemental 
fossa  from  the  central  fossa.  When  this  occurs,  there  are 
usually  triangular  supplemental  grooves  deflected  from  the 
mesial  and  distal  grooves,  to  the  mesial  and  distal  of  the  trian- 
gular ridges,  which  run  toward  the  angles  of  the  tooth  and 
separate  the  triangular  from  the  marginal  ridges,  widening 
and  deepening  the  supplemental  fossae.  A  deep  pit  is  often 
found  at  the  point  where  these  triangular  grooves  arise  from 
the  principal  grooves.  Supplemental  fossse  occur  much  more 
frequently,  or  are  more  pronounced,  in  the  mesial  than  in  the 
distal  portion  of  the  tooth,  but  in  many  examples  the  trian- 
gular ridges  are  so  widely  divided  by  sulcate,  mesial  and  distal 
grooves  that  no  supplemental  fossae  are  seen. 

113.  In  some  examples  the  lower  second  molar  presents 
dififerences  in  the  comparative  size  of  its  lobes,  and  the 
grooves  may  be  deflected  from  their  normal  course.  Occa- 
sionally, the  distal  groove  is  divided,  and  passes  over  the  distal 
marginal  ridge  in  two  divisions,  with  a  small  tubercle  between 
them.  In  poorly  developed  teeth  there  may  be  many  supple- 
mental grooves,  or  wrinkles,  running  from  the  developmental 
grooves  up  onto  the  central  inclines  of  the  ridges  and  cusps. 

114.     Fissures  occur  oftenest  near  the  central  ends  of 

the  grooves ;  though  they  may  appear  in  any  part  of  their 
length;  and  in  poorly  developed  teeth  the  supplemental 
grooves  may  be  deeply  fissured. 

115.  The  buccal  surface  of  the  lower  second  molar 
(Fig.  85)  is  convex  in  all  directions,  except  that  it  is  partially 
divided  into  two  sections,  or  ridges,  by  the  buccal  groove  (c), 
which  runs  over  onto  it  from  the  occlusal  surface.     In  many, 


92 


THE   LOWER  THIRD    MOLAR. 


this  groove  ends  near  the  center  of  the  surface  in  a  deep  buccal 
pit  (d).  This  tooth  has  no  disto-buccal  groove.  The  mesial 
and  distal  margins  converge  less  toward  the  gingival  line  than 
they  do  in  the  lower  first  molar.  The  gingival  line  is  nearly 
straight,  and  there  is  a  strong  inclination  of  the  border  of  the 
enamel  toward  it,  giving  the  appearance  of  a  gingival  enamel 
ridge. 

ii6.  The  lingual  surface  (Fig.  86)  is  similar  in  all 
points  to  that  of  the  lower  first  molar  {q.  v.,  Par.  105)  ;  but,  on 
account  of  a  much  less  convergence  of  the  mesial  and  distal 
surfaces  toward  the  lingual,  this  surface  is  nearly  as  large  as 
the  buccal  surface. 

117.  The  mesial  surface  (Fig.  87)  of  the  lower  second 
molar  is  generally  a  little  more  convex  than  in  the  lower  first 
(q.  v.,  Par.  106)  ;  but  in  other  respects  they  are  similar. 

118.  The  distal  surface  (Fig.  88)  differs  from  that  of 
the  lower  first  molar  in  not  having  the  distal  protuberance 
due  to  the  fifth  cusp.  Its  proximating  point  with  the  tooth 
distal  to  it  is  usually  central,  or  toward  the  lingual,  instead  of 
the  buccal  margin,  as  in  the  lower  first  molar.  This  surface 
is  usually  quite  regularly  and  smoothly  convex,  and  its  gingival 
line  seldom  shows  any  bucco-lingual  curvature. 

119.  The  roots  of  the  lower  second  molar  (Figs.  85  to 
89)  are  similar  to  those  of  the  first  molar;  but  the  divisions 
are  much  less  spread  and  less  grooved  on  the  mesial  and  distal 
sides.  In  many  examples  there  is  but  a  single  root,  which  is 
deeply  grooved  on  its  buccal  and  lingual  sides,  marking  out  the 
divisions.  The  root  is  much  more  irregular  in  form  than  in  the 
lower  first  molar,  and  is  often  much  curved  distally  (Fig.  89) 
or  otherwise  distorted. 

THE   LOWER  THIRD  MOLAR. 

120.  The  lower  third  molar,  called  also  the  wisdom 
tooth,  or  Dens  Sapientia,  is  the  eighth  from  the  median  line, 
and  the  last  tooth  in  the  arch.  It  proximates  the  lower 
second  molar  by  its  mesial  surface.    The  tooth  has    two   typi- 


THE    LOWER    THIRD    MOLAR.  93 

xal  forms;  the  one  is  a  four-cusped  tooth,  similar  to  the  lower 
second  molar  (Fig.  83)  ;  the  other  a  five-cusped  tooth,  similar 
to  the  lower  first  molar  (Fig.  75)  ;  but  there  are  great  varia- 
tions from  both  of  these.  ]  Indeed,  within  the  observation  of 

"the  author  the  form  of  this  tooth  is  oftener  distorted  than  any 
other. 

121.  The  four-lobed  tooth  is  the  more  common  form, 
and,  when  well  developed,  the  occlusal  surface  is  similar  to 
that  of  the  lower  second  molar.  A  supplemental  fossa  is  often 
seen,  formed  by  the  prominence  of  the  mesio-buccal  and 
mesio-lingual  triangular  ridges ;  but  in  the  distal  portion  of 
the  crown  such  a  fossa  rarely  appears.  Indeed,  in  the  four- 
cusped  lower  third  molars,  the  distal  lobes  are  generally  much 
smaller  than  the  mesial  lobes. 

122.  The  course  of  the  grooves  is  often  much  distorted, 
so  that  their  central  ends  fail  to  proximate,  as  in  Fig-.-90,-ai^ 
othef^wise.  This  renders  the  form  of  the  central  fossa  ex- 
tremely irregular.  Or  the  principal  grooves  may  be  so  con- 
fused among  a  number  of  supplemental  grooves  that  the  real 
dividing  lines  of  the  lobes  can  scarcely  be  made  out /(Fig.  91). 
In  many  of  these,  some  "oTfhe' supplemental  grooves  run  over 
the.  marginal  ridges,  corrugating  them,  or  dividing  them  into 
several  imperfect  cusps.  Occasionally  the  Vnargirial  ridges 
are  nearly  equal  in  height  all  around  the  margin  of  thte  central 
fossa,  and  the  enamel  surface  of  the  latter  r^  covered  with 
small  wrinkles,  some  of  which  may  be  deeply  fissured. 

123.     In  some  instances   the  lower  third  molar   is   very 

large,  and  in  these  the  ridges  may  be  subdivided  into  six, 
seven,  or  eight  cusps,  and  as  many  fairly  distinct  lobes ;  or, 
one  or  more  supplemental  ridges  may  appear  within  the 
limits  of  the  central  fossa  surrounded  by  grooves,  which  divide 
t'hem  from  other  parts  of  the  crown  fEig\_92).  Such  teeth 
are  usually  poorly  fonned,  and  the  grooves  deeply  fissured. 

124.  The  five-lobed  lower  third  molars  are  very  large 
teeth,  larger  than  the  second  molars,  and  very  regularly 
formed.      The  distal  lobe  is  placed  further  to  the  distal  and 


94  THE    DECIDUOUS    TEETH. 

lingual,  and  the  buccal  surface  is  more  rounded  than  in  the 
first  molars.    This  form  is  bilateral  and  hereditary. 

125.  The  buccal  surface  of  the  lower  third  molar  (Figs. 
)3>  94'  95)   is  usually  more  convex  than  in  the  other  lower 

molars,  but  otherwise  of  the  same  form.  If  four-lobed  this 
tooth  has  the  same  grooves  and  pits  as  the  lower  second ;  if 
five-lobed,    it  has  the  markings  of  the  lower  first  molars. 

126.  The  mesial,  lingual,  and  distal  surfaces  corre- 
spond with  those  of  the  other  lower  molars,  only  rather  more 
rounded ;  especially  the  distal,  which  is  often  nearly  a  true 
circle  from  buccal  to  lingual. 

127.  The  root  of  the  lower  third  molar  (Figs.  93,  94, 
95),  as  compared  with  its  crown,  is  usually  much  smaller 
than  in  the  other  lower  molars.  It  may  be  single,  or  divided 
into  two  or  more  prongs,  the  tendency  being  to  the  forma- 
tion of  two  roots,  the  same  as  in  the  other  lower  molars ;  and 
much  the  greater  number  have  the  root  in  this  form,  though 
the  single  root  is  common,  and  three  roots  (the  mesial  being 
divided)  are  not  rare.  The  root,  or  roots,  of  this  tooth  usually 
curve  distally,  sometimes  very  much,  and  are  otherwise  dis- 
torted. In  extracting,  this  inclination  of  the  roots  should  be 
kept  in  mind. 

THE    DECIDUOUS    TEETH. 

128.  These  are  the  teeth  of  early  childhood,  and  serve 
for  mastication  till  the  maxillary  bones  are  sufficiently  devel- 
oped to  accommodate  the  permanent,  the  larger  teeth  of  adult 
age.  They  are  then  removed  by  absorption  of  their  roots, 
which  allows  their  crowns  to  fall  away.  Hence  they  are  often 
called  temporary  teeth.  The  shedding  process  begins  about 
the  seventh  year,  and  is  completed  at  from  the  twelfth  to  the 
fourteenth,  the  succedaneous  teeth  taking  the  places  of  the 
deciduous.  There  are  twenty  deciduous  teeth,  ten  in  each 
jaw,  namely:  two  central  incisors,  two  lateral  incisors, 
two  cuspids,  and  four  molars.  This  may  be  expressed  by 
the  following  formula : 

1 1  C  i  M  I-  =  20 


Fig.  91. 


FiST-  93- 


Fig.  94. 


Fig-  95- 


Y. 


Fig.  90*  (Par.  122).— Left  Lower  Third  Molar,  Occlusal  Surface,  imperfect 
form,  a,  Mesio-buccal  cusp;  b.  disto-buccal  cusp;  c,  mesio-lingual  cusp;  d,  disto- 
lingual  cusp;  e,  mesial  marginal  ridge;  /,  distal  marginal  ridge;  g,  mesial  groove, 
h,  buccal  groove;  i,  lingual  groove;  /;,  distal  groove.  The  buccal  and  lingual 
grooves   do  not  meet   in   the   central   fossa   as   in  regular   forms. 

Fig.  91*  (Par.  122). —  Lower  Third  Molar,  Occlusal  Surface,  very  imperfect 
form,  a,  Mesio-buccal  cusp;  b,  disto-buccal  cusp;  c,  mesio-lingual  cusp;  d,  disto- 
lingual  cusp;  e,  mesial  marginal  ridge;  /,  distal  marginal  ridge;  g,  mesial  groove; 
h,  buccal  groove;  j,  lingual  groove;  k,  distal  groove.  Several  of  the  grooves  are 
fissured  and  are  irregular  in  form. 

Fig.  92*  (Par.  123). — Right  Lower  Third  Molar,  Occlusal  Surface,  very 
large  and  irregular  in  form,  a,  Mesio-buccal  cusp ;  b,  a  very  imperfect  disto-buccal 
cusp;  c,  mesio-lingual  cusp,  with  a  sharp  triangular  ridge,  running  very  much  to 
the  distal;  d,  disto-lingual  cusp,  standing  very  much  to  the  mesial  of  its  proper 
position;  e,  f,  a  large  supplemental  ridge,  occupying  the  middle  portion  of  the  cen- 
tral fossa;  g,  mesial  marginal  ridge;  /;,  distal  marginal  ridge;  i,  mesial  groove, 
deeply  fissured  and  with  supplemental  grooves,  also  fissured,  extending  to  the 
labial  and  lingual,  forming  a  supplemental  mesial  fossa;  k,  buccal  groove;  /,  lingual 
groove;  m,  n,  deep  fissure  on  either  side  of  the  supplemental  ridge.  There  are  a 
number  of  deep   wrinkles   running   over   the   distal   marginal   ridges. 

Fig.  93*  (Par.  125).— Right  Lower  Third  Molar,  Buccal  Surface,  with  five 
cusps,  a,  Mesio-buccal  cusp;  b,  disto-buccal  cusp;  c,  buccal  groove;  d,  buccal  pit; 
e,  disto-buccal  groove;  /,  distal  cusp;  g,  gingival  line;  h,  mesial  root;  1,  distal  root. 
In  this  tooth  the  distal  root  is  the  larger,  and  the  two  come  together  at  their 
apexes,    each   of  which   is   unusual. 

Fig.  94*  (Par.  127). — Right  Lower  Third  Molar,  with  the  roots  curved  very 
much  to  the  distal. 

Fig.  95*  (Par.  127). — Left  Lower  Third  Molar,  Buccal  Surface;  three  roots. 
a,  Mesio-buccal  cusp;  b,  disto-buccal  cusp;  c,  distal  cusp;  d,  buccal  groove;  f, 
gingival    line;   g,   mesial    root;    /;,    distal    root;    i,    supernumerary   root. 


Illustration,    ij.-^   diameters. 
8 


THE    DECIDUOUS    TEETH.  97 

There  are  no  bicuspids  in  the  diciduous  set,  and  therefore 
the  deciduous  first  molars  proximate  directly  with  the  decid- 
uous cuspids.  The  bicuspids  of  the  permanent  set  are  sue- 
cedaneous  to  the  deciduous  molars. 

129.  The  incisors  and  cuspids  of  the  deciduous  set  are 
(Eigs,-96-1:o  TOi)  similar  in  form  and  lobal  construction  with 
their  succedaneous  teeth,  but  the  deciduous  molars  give  place 
to  the  permanent  bicuspids,  which  are  of  very  dissimilar 
pattern.  The  deciduous  second  molars  (Figs.  103,  105^, 
both  upper  and  lower,  are  of  the  same  form  and  lobal  con- 
struction as  the  permanent  first  molars.  The  deciduous  first 
molars,  upper  and  lower,  have  no  similar  teeth  in  the  perma- 
nent set.  Their  form  and  the  arrangement  of  their  lobes  are 
peculiar  to  themselves ;  therefore,  the  crowns  of  these  will  be 
separately  described.     (Pars,^x34-tCLj:.5o.) 

130.  Though  the  crowns  of  the  temporary  teeth  are, 
with  the  exceptions  mentioned,  of  similar  form  and  lobal  con- 
struction as  the  permanent,  there  are  certain  minor  differences 
which  distinguish  them.  They  are  considerably  smaller  than 
the  corresponding  permanent  teeth.  This  reduction  in  size 
includes  the  whole  tooth,  and  is  such  that  it  leaves  the  general 
proportions  unchanged,  except  that  the  roots  are  proportion- 
ally longer. 

131.  The  deciduous  teeth  are,  however,  marked  with  a 
much  greater  constriction  at  their  necks.  The  enamel, 
instead  of  thinning  away  to  the  gingival  border  as  in  the  per- 
manent teeth,  retains  its  thickness  almost  to  the  gingival  line 
and  terminates  abruptly,  leaving  a  sudden  constriction  of  the 
neck  of  the  tooth.  This  varies  in  degree,  but  is  common  to 
all  of  the  deciduous  teeth,  and  distinguishes  them  from  the 
permanent  teeth. 

132.  The  buccal  and  lingual  surfaces  of  the  deciduous 
"molars  are  inclined  toward  the  occlusal  surface  much  more 

than  those  of  the  permanent,  so  that  the  immediate  occlusal 
surface  is  narrow  in  proportion  to  the  greatest  bucco-Iingual 
thickness  of  the  crown.     This  gives  the  crown  as  seen  in  the 


98  UPPER  FIRST  DECIDUOUS  MOLAR. 

mouth  the  appearance  of  being  very  long  from  mesial  to  distal ; 
though  this  characteristic  is  less  marked  in  the  upper  than  in 
the  lower  deciduous  molars  (see  Figs.  106  and  107). 

133.  The  enamel  of  the  deciduous  teeth  is  usually 
whiter  than  that  of  the  permanent  teeth,  and  they  are  probably 
of  coarser  texture.  The  difference  in  color  is  often  strongly 
contrasted  when  some  of  the  permanent  teeth,  as  the  central 
incisors,  have  taken  their  places  by  the  side  of  the  remaining 
temporary  teeth. 

UPPER    FIRST   DECIDUOUS    MOLAR. 

134.  The  occlusal  surface  of  the  upper  first  decidu- 
ous molar  (Fig.  107),  when  seen  in  the  line  of  the  long  axis  of 
the  tooth,  presents  an  irregular  quadrangular  form  in  which 
the  buccal  marginal  line  is  the  longest.  I  The— mesio-buccal 
angle  is  acute,  the  mesio-lingual  is  obtuse,  and  both  distal 
angles  are  nearly  right  angles.  The  buccal  margin  is  irregu- 
larly convex,  and  the  lingual  margin  regularly  rounded.  Both 
the  buccal  and  lingual  surfaces  are  much  inclined  centrally, 
or  toward  the  occlusal  surface. 

135.  This  tooth  has  three  lobes,  divided  by  three 
grooves.  The  mesial  (a)  and  distal  (&)  grooves  run  from  the 
mesial  to  the  distal  margin  in  a  deep  sulcus,  and  divide  the 
lingual  from  the  buccal  lobes.  Their  junction  is  in  a  pit  in 
the  central  fossa.  The  buccal  groove  (c)  rises  from  the  same 
pit,  at  the  junction  of  the  mesial  and  distal  grooves,  and  runs 
over  the  buccal  marginal  ridge  to  the  buccal  surface.  This 
groove  is  generally  without  a  sulcus ;  or,  at  most,  there  is  but 
a  slight  furrow. 

136.  The  buccal  marginal  ridge  is  a  high  cutting  edge 
which  rounds  up  from  the  mesio-buccal  angle  of  the  occlusal 
surface  and  runs  to  the  distal  and  buccal  till  it  reaches  the 
point  of  the  mesio-buccal  cusp  (d).  Its  direction  is  then  to 
the  distal,  descending  slightly  to  the  buccal  groove,  then  hori- 
zontally to  the  disto-buccal  angle  to  join  the  distal  marginal 
ridge,  the  latter  portion  forming  a  small  disto-buccal  cusp  (e). 


Fig.  96. 


Fig-  97- 


Fig:.< 


Fig.  103. 


Fig.  99. 


Fig.  100. 


Fig  loi. 


Fig.  104. 


Fig.  105. 


Fig.  106. 


Fig.  107. 


Fig.    96*  (Par.  129).— Deciduous  Upper  Central  Incisor. 

Fig.    97*  (Par.  129). —  Deciduous  Upper  Lateral  Incisor. 

Fig.    98*  (Par.  129). — Deciduous  Upper  Cuspid. 

Fig.    99*  (Par.  129).— Deciduous    Lower   Lateral   Incisor. 

Fig.  100*  (Par.  129). —  Deciduous   Lower   Lateral  Incisor. 

Fig.  ioi*  (Par.  129). — -Deciduous  Lower  Cuspid. 

Fig.  102*  (Par.  138).— Left  Upper  First  Deciduous  Molar,  Buccal  Surface 
a,  Bucco-gingival  ridge;  b,  mesio-buccal  cusp;  c,  disto-buccal  cusp;  d,  buccal 
ridge ;   e,  buccal  groove. 

Fig.  103*  (Par.  129).— Left    Upper    Second    Deciduous   Molar. 

Fig.  104*  (Par.  148).— Left  Lower  First  Deciduous  Molar,  Buccal  Surface. 
a,  Bucco-gingival  ridge;  b,  mesio-buccal  cusp;  c,  disto-buccal  cusp;  d,  buccal  ridge; 
e,   buccal    groove. 

Fig.  105*  (Par.  129).— Left  Lower  Second  Deciduous  Molar,  Buccal  Sur- 
face. 

Fig.  106*  (Par.  141). — Lower  First  and  Second  Deciduous  Molar,  Oc- 
clusal Surfaces.  The  lobes  and  grooves  of  the  lower  second  deciduous  molar  are 
the  same  as  those  of  the  permanent  lower  first  molar,  Fig.  75.  The  lower  decidu- 
ous first  molar  has  four  lobes,  a,  Mesial  groove;  b,  buccal  groove;  c,  lingual 
groove;  d,  distal  groove;  e,  mesio-buccal  cusp;  /,  disto-buccal  cusp;  g,  mesio- 
lingual  cusp;  li,  disto-lingual  cusp;  i,  mesial  fossa. 

Fig.  107*  (Par.  134). — Left  Upper  First  and  Second  Deciduous  Molars. 
The  second  deciduous  molar  has  its  grooves  and  lobes  in  the  same  form  as  those 
of  the  first  permanent  molar.  Fig.  54.  The  upper  first  deciduous  molar  has  but 
three  cusps,  a,  Mesial  groove;  b,  distal  groove;  c,  buccal  groove;  d,  mesio-buccal 
cusp;  e,  disto-buccal  cusp;   f,   lingual  cusp. 

*Illustration,    lyi   diameters. 


>r- 


LOWER    FIRST   DECIDUOUS    MOLAR.  lOI 

In  unworn  teeth,  the  buccal  groove  causes  a  marked,  but 
slight,  depression  where  it  crosses  the  ridge,  breaking  it  into 
two  cusps ;  the  mesial  being  the  larger  and  more  pointed.  This 
division  is  generally  defaced  very  early  by  wear,  so  that  the 
ridge  presents  an  almost  straight  rounded  edge. 

137.  The  lingual  cusp  (/)  is  in  the  form  of  an  elevated 
crescentic  edge  with  its  convexity  to  the  lingual,  which  runs 
from  the  mesial  termination  of  the  mesial  groove  (o)  to  the 
distal  termination  of  the  distal  groove  (b).  The  central  and 
the  lingual  inclines  of  this  cusp  are  nearly  equal  slopes,  while 
the  buccal  incline  toward  the  buccal  marginal  ridge  is  less 
abrupt  than  the  central.  The  mesial  and  distal  marginal 
ridges  are  not  marked  by  more  than  a  very  slight  thickening 
of  the  enamel,  and  are  cut  through  by  the  mesial  and  distal 
grooves. 

"^  138.  The  buccal  surface  (Fig.  102)  is  remarkable  for  its 
bucco-gingival  ridge  (a),  which  stands  boldly  out  from  the 
gingival  line  (from  one  to  three  millimeters  and  extends  from 
the  mesio-buccal  to  the  disto-buccal  angle  of  the  tooth.  At 
the  mesio-buccal  angle  it  terminates  abruptly  in  a  marked 
prominence,  and  diminishes  gradually  as  it  passes  to  the  disto- 
buccal  angle. 

139.  From  the  summit  of  the  bucco-gingival  ridge  to 
the  summit  of  the  buccal  marginal  ridge,  or  the  mesio-buccal 
cusp,  is  nearly  a  flat  surface,  except  a  slight  depression  along 
the  buccal  groove.  In  many  examples  there  is  a  slight  con- 
cavity extending  from  mesial  to  distal  along  the  occlusal  mar- 
gin of  the  bucco-gingival  ridge,  and  from  the  point  of  the 
mesio-buccal  cusp  a  strong  ridge  runs  to  the  mesio-buccal 
prominence  of  the  bucco-gingival  ridge. 

140.  The  mesial  and  distal  surfaces  are  quite  smoothly 
flattened.  The  lingual  surface  is  convex.  The  neck  presents 
the  characteristic  constriction  common  to  deciduous  teeth. 

LOWER    FIRST    DECIDUOUS    MOLAR. 

t2^i.     The  occlusal   surface  of  the  lower  first  deciduous 


I02  LOWER    FIRST    DECIDUOUS    MOLAR. 

molar  (Fig.  io6),  when  viewed  in  a  line  with  the  long  axis  of 
the  tooth,  presents  the  outline  of  a  parallelogram,  modified  by 
the  rounding  of  its  angles  and  more  or  less  convexity  of  its 
lines.  In  many,  the  distal  portion  is  broader  than  the  mesial, 
giving  the  tooth  an  ovoid  outline.  There  are  two  fossae. 
The  principal  fossa  occupies  nearly  three-fourths  of  the  distal 
portion  of  the  surface,  while  the  small  mesial  fossa  occupies  the 
immediate  mesial  portion. 

142.  The  tooth  has  four  lobes  of  irregular  form,  divided 
by  four  grooves.  These  grooves  all  run  from  the  principal 
fossa.  The  mesial  groove  (a,  a)  rises  from  the  central  pit 
and  runs  to  the  mesial,  passing  over  the  transverse  ridge  into 
the  mesial  fossa,  where  it  is  deflected  sharply  to  the  lingual, 
passing  over  the  marginal  ridge  near  the  mesio-linguo-occlusal 
angle.  This  groove  varies  considerably  in  its  course  in  dif- 
ferent examples.  In  the  principle  fossa  it  usually  inclines  to 
the  buccal  and  then  toward  the  lingual,  but  there  is  generally 
an  angle  at  the  origin  of  the  buccal  groove.  The  buccal 
groove  (b)  rises  from  the  mesial  groove,  some  distance  to  the 
mesial  of  the  pit,  and  runs  over  the  buccal  ridge  on  to  the  buc- 
cal surface,  in  a  slight  sulcus,  dividing  the  buccal  marginal 
ridge  into  two  cusps,  the  mesio-  and  disto-buccal.  Its  position 
determines  the  relative  size  of  the  buccal  lobes.  The  lingual 
groove  (c)  runs  from  the  central  pit  over  the  lingual  marginal 
ridge  on  to  the  lingual  surface,  and  is  deeply  sulcate  on  the  cen- 
tral incline  of  the  ridge.  The  distal  groove  (d)  arises  from 
the  central  pit  and  runs  over  the  distal  marginal  ridge  nearly 
centrally,  to  the  distal  surface.  It  is  often  deflected  to  the 
buccal  in  the  first  part  of  its  course  by  the  point  of  the  disto- 
lingual  triangular  ridge. 

143.  This  tooth  has  four  cusps  corresponding  with  the 
four  lobes.  The  mesio-buccal  lobe  (e)  is  very  irregular  in  its 
outline.  It  forms  the  entire  mesial  marginal  ridge,  and  from 
one-third  to  three-fourths  of  the  slopes  of  the  mesial  fossa. 
The  mesial  marginal  ridge  is  usually  high  in  young,  un- 
worn, teeth.     It  is  curved,  and  from  the  mesio-bucco-occlusal 


LOWER    FIRST   DECIDUOUS    MOLAR.  103 

angle  of  the  tooth  it  becomes  the  buccal  marginal  ridge,  and 
rises  to  the  distal  to  form  the  point  of  the  mesio-buccal  cusp 
(e).  From  the  point  of  the  cusp  it  falls  away  to  the  distal  and 
buccal  to  the  buccal  groove.  A  prominent  triangular  ridge 
descends  from  this  cusp  to  the  lingual  and  distal,  and  joins  a 
similar  triangular  ridge  from  the  mesio-lingual  cusp  (g)  to 
form  the  transverse  ridge,  thus  dividing  the  mesial  from  the 
principal  fossa.  Exceptionally,  a  deep  sulcus  divides  these 
triangular  ridges  and  connects  the  fossae.  From  the  buccal 
groove,  the  buccal  marginal  ridge  passes  almost  directly  to  the 
disto-bucco-occlusal  angle  where  it  joins  the  distal  marginal 
ridge.  In  the  central  portion  it  rises*  slightly  to  form  the  low 
disto-buccal  cusp  (/).  The  triangular  ridge  from  this  cusp  is 
usually  low,  or  wanting. 

144.  The  lingual  marginal  ridge,  (g,  h)  rises  ab- 
ruptly from  the  mesial  groove  to  the  summit  of  the  mesio-lin- 
gual cusp  (o-),and  then  falls  away  toward  the  distal  and  lingual 
to  the  lingual  groove.  In  most  specimens,  in  unworn  teeth, 
the  mesio-lingual  cusp  is  sharp,  and  its  point  is  carried  by  the 
lingual  incline  far  toward  the  central  line  of  the  tooth,  so  much 
so  as  to  be  in  marked  contrast  with  the  general  form  of  the 
lingual  cusps  of  the  lower  molars.  From  its  apex  a  triangular 
ridge  descends  to  join  that  from  the  mesio-buccal  cusp  in 
forming  the  transverse  ridge.  From  the  lingual  groove,  the 
lingual  marginal  ridge  rises  to  the  point  of  the  disto-lingual 
cusp  {h)  and  then  falls  away  in  a  curve  to  form  the  distal  mar- 
ginal ridge.  This  cusp  is  generally  rather  low,  but  varies 
much  in  these  teeth.  In  some  cases  there  is  a  sharp  triangular 
ridge  descending  into  the  central  fossa,  but  more  generally  this 
ridge  is  slight. 

145.  The  distal  marginal  ridge  is  usually  made  to  ap- 
pear prominent  by  the  depth  of  the  principal  fossa.  It  is 
crossed  near  its  center  by  the  distal  groove. 

146.  The  principal  fossa  is  generally  deep  and  well 
rounded.  The  distal  triangular  ridges,  the  only  ones  descend- 
ing into  this  fossa,  are  generally  not  prominent,  but  occasion- 


I04  LOWER    FIRST    DECIDUOUS    MOLAR. 

ally  they  are  sufficiently  so  to  render  the  fossa  very  angular. 
I  have  observed  many  in  which  the  enamel  in  this  fossa  was 
very  imperfect  and  the  bottom  of  the  fossa  broad  and  rough. 

147.  The  mesial  fossa  (^)  is  usually  sharp  and  deep, 
with  smooth  inclines,  and  has  a  central  pit  that  is  frequently  the 
seat  of  caries. 

148.  The  buccal  surface  of  the  lower  first  deciduous 
molar  (Fig.  104)  is  remarkable  for  its  prominent  bucco-gin- 
gival  ridge  (a),  which  runs  from  the  mesial  to  the  distal  mar- 
gin and  stands  out  prominently  over  the  junction  of  the  crown 
with  the  root.  From  mesial  to  distal,  this  ridge  slopes  toward 
the  occlusal  surface,  making  the  crown  longer  at  the  mesio- 
buccal  angle  than  at  the  disto-buccal.  From  this  ridge  the 
surface  slopes  rapidly  toward  the  occlusal  margin,  and  more 
rapidly  at  the  mesial  than  the  distal  portion.  From  the  mesio- 
buccal  cusp  a  strong  ridge  of  enamel  runs  to  the  more  promi- 
nent portion  of  the  bucco-gingival  ridge  near  the  mesio-buccal 
angle  of  the  tooth.  Otherwise  this  surface  is  nearly  flat.  The 
lingual  surface  is  usually  well  rounded,  but  is  broken  toward 
the  occlusal  surface  by  the  prominence  of  the  mesio-lingual 
cusp,  and  the  sulcus  of  the  lingual  groove. 

149.  The  mesial  and  distal  surfaces  are  slightly 
rounded.  The  disto-buccal  and  disto-lingual  angles  of  the 
tooth  are  about  equal  in  prominence,  but  the  mesio-buccal  and 
mesio-lingual  angles  are  very  unequal.  The  mesial  surface 
slopes  rapidly  to  the  lingual,  making  the  lingual  surface^,  much 
shorter,  mesio-distally,  than  the  buccal.  The  mesio-buccal 
angle  is  acute  and  prominent,  while  the  mesio-lingual  is  very 
obtuse  and  rounded. 

150.  The  root  of  this  molar  is  divided  into  two  prongs, 
which  are  spread  widely  apart.  They  are  thin  from  mesial  to 
distal,  and  slightly  grooved ;  and,  from  buccal  to  lingual,  broad. 
They  taper  regularly  to  broad,  flat  apexes,  which  are  occasion- 
ally bifurcated  a  short  distance. 

151.  The  roots  of  the  deciduous  teeth  are  the  same  in 
number  and  greneral  characteristics  as  in  the  teeth  of  the  same 


THE    PULP    CHAMBER.  IO5 

denomination  in  the  permanent  set,  except  that  those  of  the 
molars  are  more  divergent.  This  spreading  of  the  roots  ac- 
commodates the  crowns  of  the  permanent  bicuspids,  which  are 
developed  between  the  roots  of  the  deciduous  molars.  ^  Those 
of  the  Tower  jaw  are  thin  from  mesial  to  distal,  broad  from 
buccal  to  lingual,  and  grooved  along  their  flattened  sides.  The 
mesial  and  distal  roots  of  the  upper  deciduous  molars  are  also 
thin,  grooved,  and  widely  divergent.  The  lingual  root  stands 
boldly  to  the  lingual,  forming  a  wide  space  between  the  three, 
for  the  crowns  of  the  upper  bicuspids.  In  many  examples  the 
lingual  and  distal  roots  are  joined  by  broad  thin  connections 
for  the  greater  part  of  their  length. 

THE    PULP    CHAMBER. 

_.  152.  Every  tooth  has  a  cavity  in  the  center  of  the 
crown^  and  one  or  more  canals  extending  through  the  long 
axis  of  the  root,  or  roots,  to  the  apex.  This  cavity  contains  a 
tissue  composed  of  cellular  elements  imbedded  in  a  semi- 
gelatinous  matrix,  filling  every  part  of  the  space,  and  is  richly 
supplied  with  blood-vessels  and  nerves.  This  is  known  as  the 
pulp  of  the  tooth.* 

153.  The  central  cavity  in  the  tooth  is  usually  divided 
into  a  crown,  or  coronal  portion,  and  a  root  portion.  Its  parts 
are  familiarly  known  as  the  pulp  chamber  (crown  cavity), 
and  root  canal,  or  root  canals.  The  pulp  chamber  is  com- 
paratively large,  and  the  root  canals  are  small,  tapering  from 
the  pulp  chamber  to  a  minute  opening  at  the  apex  of  the  root, 
known  as  the  apical  foramen.  In  those  teeth  that  have 
prominent  cusps,  as  the  bicuspids  and  molars,  there  is  a  pro- 
longation of  the  pulp  toward  the  point  of  each  cusp.  These 
are  known  as  the  horns  of  the  pulp ;  and  the  prolongations  of 
the  chamber  are  designated  the  horns  of  the  pulp  chamber. 

154.  The    size    of   the   pulp   chamber   and   of  the   root 

*As  the  form  of  the  pulp  chamber  gives  the  exact  form  of  the  pulp, 
no  separate  description  of  the  pulp  will  be  given.  It  is  not  my  pur- 
pose to  give  any  histological  descriptions  in  this  work. 


I06  THE    PULP    CHAMBER. 

canals  varies  greatly  in  teeth  of  different  denominations ;  an 
also  in  different  teeth  of  the  same  denomination.  In  the  early 
formative  stages  of  the  teeth  it  is  very  large,  and  diminishes  in 
size  as  growth  proceeds,  until  the  tooth  is  fully  formed. 
Afterward  this  diminution  goes  on  slowly,  until,  in  old  age,  it 
is  often  nearly  obliterated.  In  the  formative  stage,  i.e.,  during 
the  growth  of  the  root  of  the  tooth,  the  root  canal  is  large  and 
funnel-shaped,  with  the  open  end  of  the  funnel  toward  the 
apex  of  the  root  (Fig.  72).  As  growth  proceeds,  and  the  root 
approaches  completion,  this  diminishes  rapidly  till  the  root  is 
fully  formed,  when  it  is  contracted  to  a  small  foramen.  This, 
however,  continues  to  diminish  slowly.  Therefore,  the  size 
of  the  pulp  chamber,  the  root  canals,  and  the  apical  foramen, 
are  greater  in  youth  than  in  old  age.  However,  after  adult  age 
is  reached,  the  diminution  in  size  is  usually  not  great.  During 
this  time,  the  horns  of  the  pulp  chamber  are  shortened  by  the 
same  process  of  formation  of  dentine  on  their  surface  that  is 
going  on  in  all  parts  of  the  pulp  chamber  and  root  canal. 
Therefore,  the  horns  of  the  pulp  become  shorter,  or  recede,  as 
age  advances.  Indeed,  the  whole  pulp,  very  slowly,  becomes 
smaller. 

155.  Certain  processes,  when  present,  also  serve  to 
diminish  the  size  of  the  pulp  chamber  more  rapidly ;  especially 
abrasion  of  the  teeth,  a  matter  that  seems  to  depend  largely 
upon  the  character  of  the  occlusion.  When  the  occlusion  is 
such  that  there  is  much  rubbing,  or  sliding  motion,  of  the 
teeth  against  each  other,  wear  goes  on  rapidly.  This  seems 
to  induce  depositions  of  dentine  on  the  walls  of  the  pulp 
chamber,  which  reduces  its  size ;  and,  especially,  causes  the 
recession  of  the  horns  of  the  pulp.  In  this  way,  exposure  of 
the  pulp  from  the  wearing  away  of  the  dentine  is  delayed  or 
prevented.  In  many  instances  the  pulp  chamber  is  almost  ob- 
literated in  the  molars  and  bicuspids,  and  recedes  rootwise  of 
the  gingival  line  in  the  incisors  and  cuspids.  Slowly  progres- 
sive caries  or  erosion  of  the  teeth  often  induce  similar  deposits. 

156.  In  the  incisors  and  cuspids,  the  pulp  chamber  and 


THE   PULP   CHAMBERS    OF  THE    UPPER   INCISORS.  lO/ 


THe  root  canal  are  not  sharply  differentiated.  The  latter  tapers, 
gradually,  from  the  full  size  of  the  largest  crown  portion  to  a 
small  foramen  at  the  apex  of  the  root.  In  teeth  with  more 
than  one  root,  the  transition  from  pulp  chamber  to  root  canal 
is  usually  sharply  defined,  the  former  being  very  large  as  com- 
pared with  the  pulpal  end  of  the  latter.  Indeed,  the  general 
form  of  the  pulp  is  a  diminished  counterpart  of  the  form  of  the 
surface  of  the  tooth,  except  that  it  is  in  every  way  more  slender. 

157.  Our  studies  thus  far  have  been  of  the  outer  surfaces 
of  the  teeth.  The  pulp  chambers  are  within,  and,  therefore, 
in  the  study  of  them,  dissections  must  be  made  to  expose  them 
to  view.  It  is  often  necessary  for  the  dentist  to  enter  the  pulp 
chambers  of  the  teeth  of  his  patients,  and  there  perform  deli- 
cate operations  with  a  precision  which  demands  the  most  ac- 
curate knovv^ledge  of  these  cavities.  Therefore  this  work  of 
exposure,  and  examination,  of  the  pulp  chambers  of  teeth 
should  be  thorough,  as  a  preparation  for  operations  in  the 
mouth.  The  form  of  dissection  necessary  will  be  given  in  con- 
nection with  the  teeth  as  they  are  individually  described. 

THE   PULP   CHAMBERS   OF  THE   UPPER   INCISORS. 

158.  The  pulp  chambers  and  root  canals  of  the  upper 
centra!  and  lateral  incisors  are  so  similar,  the  description  of 
one  will  do  for  all. 

Dissection. — ist.  Saw  the  tooth  through  on  the  gingival 
line,  at  the  labial  surface,  at  right  angles  with  the  long  axis. 

2d.  Saw  the  tooth  from  labial  to  lingual,  along  the  cen- 
tral line  of  the  long  axis  from  end  to  end. 

3d.  Saw  the  tooth  from  mesial  to  distal,  along  the  cen- 
tral line  of  the  long  axis  from  end  to  end. 

159.  A  very  thin  saw  in  a  strong  frame  should  be  used, 
otherwise  the  lengthwise  dissections  should  be  made  to  one 
side  of  the  central  line  in  their  first  instance,  and  afterward  the 
whole  length  of  the  pulp  chamber  exposed  by  grinding  on  a 
stone ;  or  the  lengthwise  exposure  may  be  made  by  catching 
the  tooth  in  the  vise  and  removing  one-half  with  the  file,  or  by 


I08  THE   PULP   CHAMBERS   OF  THE  UPPER  INCISORS. 

grinding  on  an  emery  wheel.  After  the  pulp  chamber  is  ex- 
posed so  that  half  of  its  concavity  remains  in  the  half  of  the 
tooth,  and  has  been  ground  smooth  and  flat,  it  should  be  inked 
on  an  inked  pad  (such  as  is  used  for  the  rubber  stamps  for 
printing) ,  and  a  print  made  from  it.  This  will  give  the  form  of 
the  tooth  and  pulp  chamber  in  silhouettes  similar  to  the  accom- 
panying illustrations.  The  printing  is  facilitated  by  sticking 
the  tooth  to  a  piece  of  hard  wax  for  convenience  in  handling. 
Ordinary  modeling  compound,  or  sealing  wax,  is  convenient 
and  effective.*  The  printing  is  usually  better  done  by  laying 
ordinary  writing  paper  on  a  sheet  of  semi-soft  rubber,  about 
one-eighth  inch  in  thickness.  This  is  specially  useful  when  the 
ground  surface  cannot  be  perfectly  flat,  as  in  curved  roots. 

i6o.  In  the  upper  central  and  lateral  incisors  (Figs. 
1 08  and  109)  there  is  no  distinct  division  of  the  pulp  cavity  into 
pulp  chamber  and  root  canal ;  but  there  is  one  straight  canal, 
from  the  interior  of  the  body  of  the  crown  -to  the  apex  of  the 
root,  of  which  the  crown  portion  is  the  larger.  In  young  teeth, 
this  has  very  distinctly  the  form  of  the  surface  of  the  tooth  and 
root,  except  that  it  is  much  more  slender.  The  largest  diame- 
ter of  the  cavity  is  about  level  with  the  gingival  line  on  the 
labial  surface.  From  this  point,  the  pulp  chamber,  or  canal, 
extends  toward  the  cutting  edge  of  the  tooth,  about  two-thirds 
the  length  of  the  crown,  sometimes  a  little  more,  often  less, 
and  ends  in  a  thin  edge,  broad  from  mesial  to  distal.  In  young 
teeth  this  edge  has  three  short  horns  (Fig.  108,  a,  b),  or  pro- 
longations, extending  -toward  the  three  small  cusps,  or  mam- 
melons,  seen  on  the  edge  of  unworn  incisors   (21). 

161.  From  the  level  of  the  gingival  line  toward  the  apex 
of  the  root  it  tapers  very  gradually  and  regularly  to  a  narrow 
canal.  Just  within  the  apex  of  the  root,  almost  at  the  end, 
there  is  usually  a  sudden  contraction  of  the  diameter  of  the 
canal,   lessening  it   from  one-third   to   one-half.     This   is   the 

*  Dr.  Cattell  has  found  that  in  teaching  it  is  very  convenient  to 
have  a  sufficient  number  of  small  pine  blocks  (^  x  ^  x  i  inch)  to 
which  he  has  pupils  cement  the  teeth  with  sealing  wax. 


an 


Fig.  io8. 


Fig.  109. 


Fig.  no. 

Fig.  108*  (Par.  160).— The  Pulp  Chamber  of  the  Upper  Central  Incisor. 
a,  b,  Mesio-distal  sections  of  young  teeth,  showing  the  three  short  horns  of  the 
pulp;  c,  mesio-distal  section  of  a  tooth  from  an  adult;  d,  e,  labio-lingual  sections. 

Fig.  109*  (Par.  160).— Pulp  Chamber  of  the  Upper  Lateral  Incisor,  a,  b, 
Mesio-distal  sections;  c,  labio-lingual  sections;  d,  labio-lingual  section  of  a  very- 
long   lateral   incisor. 

Fig.  no*  (Par.  163).— Pulp  Chamber  of  the  Upper  Cuspids,  a,  b,  Mesio- 
distal  sections;  c,  d,  labio-lingual  sections. 

*Illustration,    actual    size. 


UPPER    CUSPID PULP    CHAMBER    OF   THE    LOWER    INCISORS.    Ill 


apical  foramen ;  but  this  contraction  of  the  canal  is  not 
usually  present  for  one  or  two  years,  or  more,  after  the  tooth 
has  taken  its  place  in  the  arch  (q.  v.  Par.  154). 

162.  The  canal  becomes  smaller  from  youth  to  old  age. 
In  incisors  just  taking  their  places  in  the  arch,  I  have  found 
the  diameter  of  the  canal  at  the  gingival  line  to  be  from  one- 
fourth  to  one-'third  the  diameter  of  the  neck  of  the  tooth.  In 
early  adult  age,  the  canal  may  be  said  to  average  about  a  fourth 
the  diameter  of  the  neck  of  the  tooth,  ranging  down  as  age 
advances  to  one-fifth,  or  sixth,  and  even  to  one-tenth.  In  the 
lateral  incisor,  the  chamber  and  canal  are  a  little  smaller  than 
in  the  central,  but  larger  in  proportion  to  the  size  of  the  tooth. 

THE    UPPER    CUSPID. 

163.  The  pulp  chamber  and  root  canal  of  the  upper 
cuspid  (Fig.  no)  is  about  the  same  in  form  as  that  of  the 
central  and  lateral  incisors,  except  that  the  coronal  extremity 
has  the  central  horn  much  extended  toward  the  apex  of  the 
cusp  of  the  tooth,  and  the  mesial  and  lateral  horns  are  prac- 
tically absent.  The  canal  is  proportionately  somewhat  smaller. 
However,  this  tooth  is  often  somewhat  flattened  at  the  neck, 
the  long  diameter  being  from  labial  to  lingual.  In  this  case 
the  pulp  canal  at  the  neck,  and  from  thence  toward  the  apex 
of  the  root,  is  also  much  flattened  in  the  same  direction,  but 
is  progressively  rounded  as  the  apex  is  approached.  In  some 
examples,  the  labio-lingual  diameter  of  the  canal  is  double  the 
mesio-distal.  As  age  advances,  and  the  canal  becomes  smaller, 
the  opening  is  occasionally  reduced  to  a  mere  slit. 

PULP    CHAMBER  OF  THE  LOWER  INCISORS. 

164.  (Fig.  III.)  The  coronal  portions  of  the  pulp 
chamber  of  the  lower  incisors  is  much  flattened.  At  the 
level  of  the  gingival  line,  the  long  diameter  is  from  labial  to 
lingual.  The  chamber  extends  toward  the  cutting  edge  of  the 
tooth,  about  two-thirds  the  length  of  the  crown,  and  in 
this  extension  its  diameter  is  progressively  diminished  from 
labial  to  lingual,  and  extended  from  mesial  to  distal,  follow- 

9 


112  PULP   CHAMBER   OF  THE   LOWER  CUSPID. 

ing  the  contour  of  the  surface  of  the  tooth,  and  ends  in  a  thin 
edge.  In  young  teeth  this  has  three  short  projections  toward 
the  mammelons  on  the  cutting  edges  of  the  young,  unworn 
teeth.  The  root  has  usually  a  narrow  slit-like  opening  for 
the  greater  portion  of  its  length  {d,  g),  corresponding  with  tire 
form  of  the  flattened  roots.  In  many  instances,  however,  the 
root  canal  is  divided  into  two  portions,  or  canals,  for  a  part 
of  its  length  {e,  f).  In  the  adult  these  canals  are  usually  very 
small.  The  point  of  separation  into  two  canals  is  irregular, 
but  is  usually  slightly  root-wise  from  the  level  of  the  gingival 
line.  It  may  occur  at  about  the  level  of  the  gingival  line,  or 
the  canal  may  remain  single  for  half  the  length  of  the  root, 
and  then  be  divided  for  a  space,  the  two  uniting  again  before 
reaching  the  apex.  Generally,  there  is  but  one  apical  foramen. 
Instances  occur  in  which  there  are  two,  each  canal  remaining 
distinct  to  the  end.  As  age  advances,  the  canals  of  the  lower 
incisors  often  become  very  minute. 

PULP   CHAMBER  OF  THE   LOWER  CUSPID. 

165.  The  pulp  chamber  and  the  root  canal  of  the  lo^ve^ 
cuspid  (Fig.  112)  are  variable  in  size  and  form.  At  the  neck 
of  the  tooth  the  chamber  is  usually  irregularly  flattened,  with 
the  longer  diameter  from  labial  to  lingual,  and  the  labial  por- 
tion wider  than  the  lingual.  The  coronal  portion  extends 
about  two-thirds  of  the  length  of  the  crown  toward  the  point 
of  the  cusp,  ending  in  a  point,  or  horn,  which  is  often  very 
slender.  The  form  of  the  root  portion  of  the  canal  depends 
on  the  form  of  the  root.  It  is  sometimes  nearly  round,  but 
more  frequently  it  is  sharply  flattened  for  the  greater  portion 
of  its  length,  becoming  more  rounded  toward  the  apex.  Occa- 
sionally, this  canal  is  divided  for  a  part  of  the  length  of  the 
root.  Also,  the  root  is  sometimes  divided,  a  very  small  prong 
appearing  on  its  lingual  side.  In  this  there  is  usually  a  very 
small  canal  that  is  difficult  to  enter  with  a  broach.  In  some 
lower  cuspids  the  canal  is  very  small  (a),  in  others  very  large 
(6).    In  a  few  instances  I  have  seen  it  more  than  one-third  the 


Fig.  112. 


Fig.  Ill*  (Par.  164). — Pulp  Chamber  of  the  Lower  Central  and  Lateral 
Incisors,  a,  b,  c,  Labio-lingual  sections,  showing  differences  of  form  of  the  pulp 
chamber;  d,  mesio-distal  section;  e,  f,  labio-lingual  sections,  showing  the  more 
usual  forms  of  the  pulp  chamber;  g,  mesio-distal  section,  showing  large  pulp 
chamber. 

Fig.  112*  (Par.  165). — Pulp  Chamber  of  the  Lower  Cuspids,  a,  Labio-lingual 
section,  showing  a  small  chamber;  b,  labio-lingual  section,  showing  a  very 
large  pulp  chamber;  c,  mesio-distal  section. 


'Illustration,    actual     size. 


PULP    CHAMBER   OF   THE  UPPER   FIRST  BICUSPID.  II5 

diameter  of  the  root  in  the  adult.  In  this  case  the  diameter 
of  the  canal  is  greater  than  the  thickness  of  the  walls  of  den- 
tine and  cementum  by  which  it  is  inclosed.  This  renders  the 
pulp  very  liable  to  exposure  in  excavating  carious  cavities. 

PULP    CHAMBERS    OF   THE  BICUSPIDS. 

166.  Dissections. — ist.  Divide  the  crown  from  the  root 
on  the  gingival  line  with  a  fine  saw. 

2d.  Divide  the  tooth  from  buccal  to  lingual  through  its 
length  with  a  fine  saw,  or  remove  the  distal  half  of  the  tooth 
with  the  file  or  stone.  These  two  dissections  will  usually 
exhibit  the  pulp  chamber  and  root  canals  sufficiently,  though 
in  the  single-rooted  teeth  with  two  canals  it  is  better  to  divide 
the  root  crosswise  at  the  middle  of  its  length,  or  at  several 
points. 

PULP   CHAMBER  OF  THE  UPPER   FIRST  BICUSPID. 

167.  The  pulp  chamber  and  root  canals  of  this  tooth 
differ  from  those  of  the  incisors  and  cuspids  by  having  the 
coronal  chamber  distinguished  sharply  from  the  root 
canals  (Fig.  113,  d,  e).  The  chamber  is  centrally  located  in 
the  long  axis  of  the  crown  of  the  tooth,  the  axial  walls  being 
about  equal  in  thickness.  The  center  of  the  pulp  chamber  is 
about  level  with  the  gingival  line,  or  a  little  toward  the  occlusal 
surface.  The  occlusal  walls  are  thicker  than  the  axial,  and 
vary  in  thickness  from  one-third  to  two-thirds  of  the  length 
of  the  crown  of  the  tooth.  The  form  of  the  pulp  corresponds 
closely  with  the  form  of  the  tooth.  A  horn  extends  from 
the  coronal  portion  toward  the  apex  of  each  cusp.  The 
buccal  horn  rises  from  the  extreme  buccal  part  of  the  pulp, 
while  the  lingual  horn  rises  from  the  extreme  lingual  por- 
tion. Sometimes,  especially  in  teeth  with  long  cusps,  they  are 
very  long  and  slender,  extending  far  toward  the  points  of  the 
cusps,  and  in  rare  cases  almost,  or  even  quite,  to  the  enamel. 
As  age  advances,  they  become  shorter,  and  in  old  age  have 
almost  disappeared.     In  thick-necked  teeth  with   short  cusps 


Il6         PULP   CHAMBER  OF   THE   UPPER   SECOND   BICUSPID. 

the  horns  of  the  pulp  chamber  are  short,  and  the  occlusal  wall 
is  usually  very  thick. 

The  root  canals  in  upper  first  bicuspids  that  have  two 
roots  pass  from  the  pulp  chamber  through  the  center  of  each 
root  to  its  apex,  and  are  known  as  the  buccal  and  lingual 
root  canals  (e).  The  buccal  canal  arises  from  the  extreme 
buccal  side  of  the  pulp  chamber,  and  the  lingual  canal  from 
the  extreme  lingual  side,  and  their  course  is  almost  parallel 
with  the  walls  of  these  two  portions  of  the  pulp  chamber.  The 
floor  of  the  chamber  is  rounded  over  in  an  arch  from  one  canal 
to  the  other.  Each  canal  begins  in  a  funnel-shaped  opening 
leading  into  a  narrow  round  canal,  which  tapers  gradually  to 
the  apical  foramen.  Many  of  the  upper  first  bicuspids  have 
only  one  root ;  but  they  generally  have  two  root  canals  almost 
exactly  similar  to  those  with  two  roots.  Occasionally,  how- 
ever, these  come  together  and  end  in  one  apical  foramen,  or 
there  may  be  a  communication  between  the  two  canals  in  some 
part  of  their  course  (d).  More  rarely,  the  upper  first  bicuspid 
has  one  broad  (from  buccal  to  lingual),  flat  canal  passing 
through  the  whole  length  of  its  single  root.  Sometimes  this 
is  divided  near  the  apex  (b). 

PULP   CHAMBER  OF  THE  UPPER  SECOND  BICUSPID. 

i68.  The  pulp  chamber  of  the  upper  second  bicuspid 
(Fig.  114)  is  similar  to  that  of  the  first  {q.  v.,  Par.  167),  but 
the  horns  of  the  pulp  are  usually  shorter.  In  this  tooth  there  is 
generally  but  a  single  root  canal  {e,  f).  This  is  approached 
by  an  opening  that  is  broad  bucco-lingually,  and  tapers  grad- 
ually toward  the  apex  of  the  root,  ending  in  a  narrow  apical 
foramen.  The  canal  is  often  quite  large,  and  the  demarkation 
of  the  pulp  chamber,  as  distinguished  from  the  root  canal, 
very  indistinct,  or  entirely  absent.  Examples  are  not  infre- 
quent, however,  in  which  there  are  two  root  canals  in  the 
single  root  {d).  They  are  then  similar  to  those  of  the  first 
bicuspid ;  but,  sometimes,  the  two  canals  end  in  a  common 
apical  foramen  (a). 


Fig.  115. 


Fig.  116. 


Fig.  113*  (Par.  167). — Pulp  Chamber  and  Root  Canals  of  the  Upper  First 
Bicuspids,  b,  Bucco-lingual  section  of  single-rooted  tooth,  witli  single  canal  di- 
vided near  the  apex  of  the  root;  a,  cross-section  of  the  same,  mid-length  of  the  ' 
root;  d,  bucco-lingual  section  of  a  single-rooted  tooth  with  two  canals,  which  con- 
nect at  one  point;  c,  cross-section  of  the  same,  a  little  rootwise  from  the  pulp 
cham.ber;  e,  bucco-lingual  section  of  double-rooted  tooth,  showing  the  more  usual 
form  of  the   chambers  and  canals. 

Fig.  114*  (Par.  168). — Pulp  Chamber  and  Root  Canals  of  the  Upper  Second 
Bicuspid.  a,  Bucco-lingual  section,  showing  chamber  with  long,  slender  horn, 
also  two  canals,  which  unite  in  the  apical  third  of  the  root;  b,  cross-section  of  a 
root  with  two  canals;  c,  cross-section  of  a  root  with  a  single  large  canal;  d,  bucco- 
lingual  section  of  a  single  root  with  two  canals;  e,  f,  bucco-lingual  sections,  show- 
ing the  more  usual  form  of  the  pulp  chamber  and  root  canal  of  this  tooth. 

Fig.  115*  (Par.  169). — Pulp  Chamber  and  Root  Canals  of  the  Dower  First 
Bicuspid,  a,  Bucco-lingual  section,  showing  the  more  usual  form;  b,  bucco-lingual 
section,  showing  a  peculiar  and  very  unusual  division  of  the  root  canal;  c,  cross- 
section  in  the  body  of  the  root. 

Fig.  116*  (Par.  169). — Pulp  Chamber  and  Root  Canal  of  the  Lower  Second 
Bicuspid,  a,  b,  Bucco-lingual  sections,  showing  the  more  usual  forms  of  the 
chamber    and    canal    in    this    tooth. 


"Illustration,   actual   size. 


PULP    CHAMBERS LOWER    BICUSPIDS UPPER    MOLARS.    1 19 


PULP   CHAMBERS  OF  THE  LOWER  BICUSPIDS. 

169.  The  pulp  chambers  of  the  lower  bicuspids  (Figs. 
115  and  116)  seldom  show  a  marked  distinction  from  the  root 
canals.  There  is,  however,  usually  a  coronal  bulbous  portion 
which  connects  with  the  pulp  canal  proper  by  an  extended 
funnel-shaped  constriction  (a,  b).  In  the  lower  first  bicus- 
pid, the  coronal  extremity  ends  in  a  horn,  which  extends 
toward  the  point  of  the  buccal  cusp.  This  horn  may  be  short 
and  obtuse,  or  long  and  pointed.  There  is,  generally,  a  well- 
marked  protrusion  toward  the  lingual  cusp,  but  no  extended 
horn.  It  is  rather  an  enlargement  of  the  bulb  in  that  direc- 
tion. In  the  lower  second  bicuspid  this  protrusion  is  more 
considerable,  and  in  some  examples  it  is  elongated  into  a 
slender  point,  especially  in  young  teeth  (Fig.  ii6,  h).  In  the 
three-cusped  lower  second  bicuspids  (Par.  62,  Fig.  49)  there 
are  two  of  these  on  the  lingual  side,  spreading  toward  the 
mesial  and  distal.  They  are  generally  short,  but  by  their 
protrusion  are  brought  rather  nearer  the  surface  of  the  tooth 
than  other  horns  of  the  pulp,  and  are;  therefore,  more  liable 
to  be  opened  into  when  excavating  proximate  cavities. 

170.  The  root  canals  of  the  lower  bicuspids  are  usually 
large  in  the  first  half,  tapering  to  a  fine  canal  in  the  apical 
third,  of  their  length.  The  canal  of  the  lower  first  bicuspid 
is  usually  nearly  round,  and  that  of  the  second  is  considerably 
flattened ;  and  in  both  they  are  usually  straight.  Bifurca- 
tions of  these  canals  are  rare,  but  occur  occasionally.  In  the 
illustrations  (Fig.  115,  b)  one  is  shown  dividing  in  such  a 
way  that  the  division  would  not  be  likely  to  be  detected  by  a 
broach. 

PULP   CHAMBERS  OF  THE   UPPER   MOLARS. 

171.  Dissections. — ist.  With  a  fine  saw,  separate  the 
crown  from  the  root  level  with  the  gingival  line. 

2d.  Cut  away  the  mesial  surface  of  the  crown  and  the 
mesial  surface  of  the  mesial  and  lingual  roots  with  the  file 
or  a  corundum  stone,  till  the  canals  in  each  are  fully  exposed. 


I20  PULP    CHAMBERS    OF    THE    UPPER    MOLARS. 

As  the  mesial  root  is  generally  curved,  some  care  is  required 
to  fully  expose  the  full  length  of  the  canal  without  cutting 
too  far  in  the  central  portion  of  its  length.  If  the  curved  sur- 
face is  made  smooth,  good  prints  can  generally  be  made  by 
using  a  piece  of  semi-soft  rubber  under  the  paper,  and,  while 
pressing  it  to  the  paper,  rolling  the  tooth  so  as  to  bring  all  of 
the  length  of  the  curved  surface  in  contact. 

3d.  Cut  away  the  buccal  surface  so  as  to  expose  the 
pulp  chamber  and  canals  of  the  two  buccal  roots,  observing 
the  same  precautions  as  in  the  second  dissection. 

In  the  first  dissection  both  crown  and  root  should  be 
examined.  First,  clean  the  portion  of  the  chamber  in  the 
crown,  to  study  carefully  its  horns  and  its  general  shape  or 
contour  with  relation  to  the  outer  surface  of  the  tooth.  The 
root  canals  should  be  cleaned  with  the  broach,  and  their  size 
and  direction  carefully  studied;  also,  the  position  of  the  open- 
ings leading  from  the  pulp  chamber  should  be  studied  with 
regard  to  their  relation  to  the  several  points  of  the  surface  of 
the  crown.  This  latter  is  especially  important.  Several  dis- 
sections should  be  made  of  each  of  the  upper  molars. 

4th.  Grind  away  the  root  portion  of  the  first  dissection, 
printing  occasionally  till  the  bifurcation  of  the  roots  is  reached. 

172.  The  pulp  chamber  of  the  upper  molars  is  very 
distinct  from  the  pulp  canals,  the  latter  often  leaving  the 
former  by  very  small  openings  (Fig.  117).  The  average  diam- 
eter of  the  pulp  chamber  is  about  equal  to  the  thickness  of 
the  axial  wall  by  which  it  is  surrounded,  sometimes  more, 
sometimes  less.  The  occlusal  wall  is  usually  considerably 
thicker.  The  form  of  the  pulp  chamber  is  generally  similar 
to  that  of  the  crown  of  the  tooth ;  but  the  horns  in  the  young 
tooth  are  often  quite  slender  as  compared  with  the  cusps,  and 
penetrate  far  toward  the  enamel.  The  length  of  these  dimin- 
ishes as  age  advances.  In  teeth  much  flattened  mesio-distally, 
as  often  occurs  in  the  upper  first  molars,  and  especially  with 
the  second,  the  equal  thickness  of  the  axial  walls  is  usually 
maintained  pretty  closely,  so  that  the  flattening  of  the  pulp 
chamber  seems  out  of  proportion  to  the  form  of  the  tooth. 


PULP    CHAMBERS    OF   THE    UPPER    MOLARS.  121 

173.  The  floor  of  the  pulp  chamber  is  rounded  or 
arched  in  the  center,  and  falls  away  toward  the  mouths  of  the 
canals.  The  latter  are  situated  in  the  position  of  the  angles 
of  a  triangle  (the  molar  triangle.  Figs.  ii8  and  119),  the 
mesial  line  of  which  is  the  longest,  the  buccal  the  shortest, 
and  the  distal  the  intermediate  length.  For  the  upper  first 
molar,  this  triangle  is  well  shown  in  the  illustrations  repre- 
senting sections  a  little  rootwise  from  the  floor  of  the  pulp 
chamber  (c).  This  is  best  seen  in  the  specimen  itself;  and  the 
position  and  the  direction  of  the  canals,  with  relation  to  the 
walls  of  the  pulp  chamber  and  the  main  points  of  the  surface 
of  the  crown,  should  be  carefully  studied. 

174.  The  opening  into  the  lingual  root  (Fig.  117,  b)  is 
the  simplest  and  most  direct.  Generally,  it  begins  in  a  funnel- 
shaped  opening  inclining  to  the  lingual,  which  quickly  narrows 
to  the  dimensions  of  a  moderately  small  canal,  and  continues 
to  taper  to  the  apical  foramen.  It  is  usually  straight,  or  but 
slightly  curved. 

175.  The  opening  into  the  mesial  canal  is  under  the 
mesio-buccal  cusp,  close  against  the  mesio-buccal  angle  of 
the  pulp  chamber.  It  often  happens  that  this  canal  begins 
in  a  groove  in  the  angle  of  the  chamber  (Fig.  119,  b),  making 
this  the  thinnest  point  in  the  dentinal  walls  surrounding  it, 
In  young  teeth,  the  mouth  of  the  canal  is  of  a  flattened  funnel- 
shape,  which  is  quickly  contracted  into  a  very  fine  canal;  but 
in  the  adult,  it  often  begins  as  a  fine  canal.  Its  course  at  first 
is  to  the  buccal  and  mesial,  and  then  curves  to  the  distal.  It 
is  usually  distinctly  flattened,  and  often  has  a  thin  edge  to  the 
lingual.  It  is  often  a  very  difficult  canal  to  clean  with  a 
broach.  To  find  this  canal  the  point  of  the  broach  should 
be  directed  into  the  mesio-buccal  angle  of  the  pulp  chamber; 
and,  while  held  against  the  wall  within  this  angle,  it  is  slid 
toward  the  root.    It  will  rarely  fail  to  glide  into  the  canal. 

176.  The  distal  canal  usually  begins  abruptly  as  a  fine 
opening  (Fig.  117,  a^  c),  situated  at  the  disto-buccal  angle  of 
the  floor  of  the  pulp  chamber  (Figs.  118  and  119)  ;  so  that  a 


122  PULP   CHAMBERS  OF   THE   UPPER  MOLARS. 

broach  pressed  into  that  angle  will  easily  glide  into  it.  But 
in  some  instances,  especially  in  the  upper  second  molars,  the 
opening  is  in  the  floor  of  the  pulp  chamber  at  a  little  distance 
from  the  immediate  angle  toward  the  center  of  the  floor,  and 
then,  in  positions  which  limit  the  use  of  the  eye,  it  is  often 
difficult  to  find.  In  teeth  much  flattened  at  the  neck,  the 
opening  of  this  canal  may  begin  very  close  to  the  mouth  of 
the  mesial  canal  (Fig.  120,  a),  or  close  against  the  distal  wall 
of  the  chamber,  half-way  from  the  buccal  to  the  lingual  wall, 
or  anywhere  between  this  point  and  the  disto-buccal  angle. 
The  first  direction  of  the  canal  will  vary  according  to  its  posi- 
tion. If  it  is  found  in  a  fairly  well-defined  disto-buccal  angle 
of  the  chamber,  its  direction  will  be  a  little  inclined  to  the 
distal,  and  the  broach  will  penetrate  it  easily ;  if  in  the  floor 
of  the  chamber,  it  will  sometimes  be  straight,  as  in  the  former 
case ;  but  more  generally  the  first  direction  will  be  to  the  distal 
and  buccal,  with  considerable  curve  afterward.  If  found  close 
to  the  mesial  canal,  its  course  is  usually  first  sharply  to  the 
distal,  when  it  curves  rather  abruptly  toward  the  apex  of  root. 
If  found  along  a  smooth  or  curved  distal  wall,  the  course  will 
generally  be  to  the  distal  and  buccal,  with  but  little  curve. 
This  canal  is  usually  very  fine  from  its  beginning,  and  almost 
or  quite  round. 

177.  While  the  canals  are  similar  in  all  of  the  upper 
molars,  there  are  differences  in  the  form  of  the  floor  of  the 
pulp  chamber  that  may  be  briefly  generalized.  The  pulp 
chamber  of  the  upper  second  molar  (Fig.  120)  is  usually  much 
more  flattened  from  mesial  to  distal  than  in  the  first  molar. 
This  changes  the  relation  of  the  mouths  of  the  canals  some- 
what, rendering  the  distal  angle  of  the  triangle  formed  by 
them  more  obtuse,  and  brings  the  mouth  of  the  distal  canal 
nearer  the  mesial  line  of  the  triangle,  so  that  it  seems  to  be 
found  along  the  distal  wall  of  the  narrowed  chamber.  In 
others,  it  is  found  in  the  extreme  buccal  portion  crowded  close 
against  the  mouth  of  the  mesial  canal. 

178.  The  position  of  the  openings  of  the  canals  in  the 


Hfcf 


Fig.  117. 


dftftood 


a  b  e 

Fig.  118. 


a  t> 


Fig.  119. 


H  a 


Fig.  120. 


Fig.  121. 


Fig.  117*  (Par.  172). — Pulp  Chamber  and  Root  Canals. of  the  Upper  First 
Molar,  a,  c,  Mesio-distal  sections,  showing  the  pulp  chamber  and  the  canals  in 
the  mesial  and  distal  roots;  b,  bucco-lingual  section,  showing  the  pulp  chamber 
and  the  canals  in  the  mesial  and  lingual  roots;  d,  bucco-lingual  section,  showing 
the  chamber  and  the   canals  in  the   distal  and  lingual  roots. 

Figs.  118,*  119*  (Par.  173). — Pulp  Chamber  and  Root  Canals  of  the  Upper 
First  Molars,  cross  sections,  a,  Centrally  through  the  pulp  chamber;  b,  section 
just  at  the  floor  of  the  pulp  chamber;  c,  section  a  little  rootwise  from  the  pulp 
chamber,   showing  the  canals  and  the  form  of  the  molar  triangle. 

Fig.  120*  (Par.  177). — Pulp  Chamber  and  Root  Canals  of  the  Upper  Sec- 
ond Molar,  a,  Mesio-distal  section,  showing  pulp  chamber  and  the  canals  in  the 
mesial  and  distal  roots;  b,  bucco-lingual  section,  showing  the  chamber  and  the 
canals    in   the    distal   and   lingual   roots. 

Fig.  121*  (Par.  178). — Pulp  Chamber  and  Root  Canals  in  the  Upper  Third 
Molar,  a,  Bucco-lingual  section,  showing  pulp  chamber  and  the  canals  in  the 
mesial  and  lingual  roots;  b,  mesio-distal  section  of  a  single  rooted  tooth,  showing 
the  form  of  the  pulp  chamber  and  the  mesial  and  distal  root  canals. 

*Illustration,    actual    size. 


I'ULl'    CHAMBERS    OF    THE    LOWER    MOLARS.  I25 

upper  third  molar  (Fig.  121)  is  usually  much  the  same  as  in 
the  first  and  second,  varying  so  as  to  resemble  either.  Occa- 
sionally there  is  more  than  the  usual  number,  and  others  with 
only  one  or  two.  When  there  is  but  one,  it  is  commonly  quite 
large.  Four,  five,  or  even  seven  or  eight,  are  sometimes 
found. 

PULP    CHAMBERS    OF    THE    LOWER    MOLARS. 

179.  Dissections. — ist.  Saw  the  tooth  through  the  gin- 
gival line  dividing  the  crown  from  the  root.  This  cut  will 
pass  through  the  body  of  the  pulp  chamber  and  give  a  good 
view  of  the  roof  and  floor,  and  a  good  idea  of  the  general  form. 
The  root  canals  should  be  cleaned  and  examined  with  the 
broach. 

2d.  Saw  the  tooth  through  from  end  to  end  centrally 
from  mesial  to  distal,  or  grind  or  file  away  the  buccal  side  till 
the  pulp  chamber  and  the  root  canals  are  exposed.  As  there 
are  usually  two  canals  in  the  mesial  root,  an  exact  central  cut 
from  mesial  to  distal  will  generally  fail  to  expose  the  canals, 
and  the  cut  will  be  better  made  at  a  slight  angle,  so  as  to  ex- 
pose either  the  buccal  or  lingual  canal  of  the  mesial  root. 

3d.  Grind  or  file  away  the  mesial  surface  of  the 
crown  and  root  till  the  pulp  chamber  and  the  whole  length  of 
the  canals  in  the  mesial  root  are  exposed.  As  this  root  is  usu- 
ally curved,  the  cutting  must  be  done  with  care,  and  the  curve 
followed. 

4th.  Cross-sections  of  the  roots  should  be  made  at 
intervals.  An  excellent  study  is  to  begin  grinding  at  the  apex 
of  the  roots,  printing  occasionally,  and  continuing  the  grinding 
until  the  pulp  chamber  is  reached.  This  will  display  cross-sec- 
tions, at  intervals,  of  the  entire  root  canals.  Enough  of  these 
dissections  should  be  made  of  each  of  the  lower  molars  to  make 
the  student  familiar  with  each  class. 

180.  The  pulp  chambers  of  the  lower  molars  (Figs. 
122,  123,  124)  has  the  same  general  form  as  the  surface  of  the 
crown,  but  is  generally  rather  more  angular.     The  wall  of  the 


126  PULP  CHAMBERS  OF  THE  LOWER   MOLARS. 


chamber  toward  the  occlusal  surface  is  convex  toward  the 
pulp ;  the  horns  extend  from  the  extreme  angles  toward  the 
apex  of  each  cusp.  The  floor  through  the  central  portion  is 
arched  or  convexed  mesio-distally,  and  concave  bucco-lingu- 
ally.  The  mesial  wall  of  the  cavity  is  flat,  and  longer  than  the 
distal.  The  mesio-buccal  and  mesio-lingual  angles  are  sharp 
and  projecting,  while  the  distal  angles  are  rounded  (Fig.  123, 
d,  g).  The  size  of  the  chamber  varies  much.  In  youth  its 
diameter  is  often  as  much  as  two-fifths  of  the  crown  and  sel- 
dom less  than  one-third.  This  diminishes  as  age  advances, 
and  in  old  age  it  is  often  very  small,  or,  especially  where  there 
has  been  considerable  abrasion  of  the  teeth,  the  pulp  chamber 
may  be  almost  obliterated. 

181.  The  root  canals  of  the  lower  molars  proceed  from 
the  mesial  and  distal  portions  of  the  pulp  chamber  (Fig.  122, 
a,  b) .  The  mesial  canal,  at  its  mouth,  is  usually  about  as 
broad  from  buccal  to  lingual  as  the  whole  breadth  of  the  cham- 
ber, including  its  angular  projections.  Either  at,  or  a  little 
rootwise  from  the  floor  of  the  pulp  chamber,  it  is  usually  di- 
vided into  two  very  small  canals  which  diverge  at  first,  and  ap- 
proach each  other  afterward,  but  usually  remain  distinct,  each 
ending  in  its  own  apical  foramen  (Fig.  122,  c).  Occasionally, 
however,  they  are  united  in  the  apical  third  of  the  root,  and 
end  in  a  common  apical  foramen.  Again,  there  may  be  a  com- 
munication between  them  in  the  apical  portion  of  the  root, 
each  canal  remaining  otherwise  complete  in  itself.  A  few  have 
one  broad  flattened  canal  (Fig.  123,  d,  e,  f).  These  canals  are 
usually  minute,  and  very  difficult  to  thoroughly  clean  with  the 
broach,  though  the  mesio-buccal  canal  is  usually  easily  found, 
if  the  pulp  chamber  is  thoroughly  opened.  By  placing  the 
point  of  the  broach  in  the  mesio-buccal  angle  of  the  cham- 
ber and  pushing  it  gently  on,  it  will  generally  glide  into  the 
canal.  The  first  direction  inclines  to  the  mesial  and  buccal, 
after  which  it  curves  to  the  distal  and  lingual  (Fig.  122,  c). 
Generally,  these  curves  are  easy,  without  short  bends.  The 
broach  easily  glides   into   the   mesio-lingual  canal  In-  placing 


Fig.  122. 


g  h 

Fig.  123. 


9 


Fig.  124. 


Fig.  125. 

Fig.  122*  (Par.  i8o).— Pulp  Chamber  and  Root  Canals  of  the  Lower  First 
Molar,  a,  b,  Mesio-distal  sections,  showing  the  form  of  the  pulp  chamber  and 
root  canals;   c,   bucco-Iingual  section,  showing  the  canals  in  the   mesial  root. 

Fig.  123*  (Par.  180).— Cross-sections  through  the  Crown  and  Root  of  the 
Lower  First  Molar,  showing  the  pnlp  chamber  and  root  canals,  rf,  g,  Sec- 
tions through  the  pulp  chamber;  e,  h,  sections  a  little  rootwise  from  the  pulp 
chamber;   /,   i,    sections    near   apex   of  root. 

Fig.  124*  (Par.  180).— Pulp  Chamber  and  Root  Canals  of  the  Lower  Sec- 
ond Molar.  ,  a,  c,  Mesio-distal  sections,  showing  the  form  of  the  pulp  chamber 
and  root  canals;  b,  bucco-lingual  section  of  the  distal  root  and  crown;  d,  bucco- 
lingual  section  through  the  mesial  root  and  crown,  showing  two  canals  with  com- 
munication in  the  apical  third  of  the  root.  This  cornmunication  is  not  very  com- 
mon. 

Fig.  125*  (Par.  182).— Pulp  Chamber  and  Root  Canals  of  the  Lower  Third 
Molar,     a,   c.   In  double-rooted  teeth;  b,   single-rooted  teeth. 


'Illustration,   actual   size. 
10 


VARIATIONS    OF    THE    FORM    OF    PULP    CHAMBERS.  I29 

the  point  in  the  mesio-lingual  angle  of  the  pulp  chamber 
and  sliding  it  toward  the  root.  The  first  inclination  is  to  the 
mesial,  but  occasionally  to  the  lingual,  after  which  it  curves 
to  the  distal  and  buccal. 

182.  The  distal  canal  is  approached  by  a  funnel-shaped 
opening,  of  which  the  central  part  of  the  distal  wall  of  the 
pulp  chamber  becomes  a  portion.  Its  direction  is  a  little  to 
the  distal,  and  is  generally  very  nearly  straight  to  the  apex. 
At  first,  it  is  flattened,  with  the  long  diameter  from  buccal  to 
lingual,  and  progressively  becomes  rounded,  and  tapers  regu- 
larly to  the  apical  foramen.  It  is  generally  much  larger  than 
the  canals  of  the  mesial  root,  and  is  easily  cleaned  with  the 
broach.  If  the  mouth  is  wide  open,  and  the  handle  of  the 
broach  brought  against  the  upper  central  incisors  with  the 
point  directed  against  the  posterior  wall  of  the  pulp  chamber, 
it  will  easily  glide  into  the  canal,  and  pass  to  the  apical  fora- 
men. This  particular  position  for  easily  entering  the  distal 
canal  is  important  for  all  the  lower  molars.  Occasionally,  the 
lower  third  molar  has  but  one  root  canal  (Fig.  125,  b) ,  which 
is  then  generally  very  large.  More  rarely,  only  a  single  canal 
will  be  found  in  the  lower  second  molar,  but  generally  the 
canals  of  the  second  and  third  lower  molars  are  similar  to 
those  of  the  first.  The  pulp  chambers  ars  usually  smaller,  and 
oftener  irregular  in  outline.  The  lower  third  molar  has,  occa- 
sionally, a  very  large  pulp  chamber. 

VARIATIONS    OF    THE    FORM    OF    PULP    CHAMBERS. 

183.  Many  variations  of  form  occur  in  the  pulp  cham- 
bers and  root  canals.  The  roots  of  the  teeth  may  be  abnor- 
mally crooked;  and  then  the  canals  will  be  abnormally 
crooked.  In  many  instances,  the  pulp  chamber  will  have  in  it 
secondary  formations,  called  nodules,  which  may  be  ad- 
herent to  the  walls,  or  block  the  mouths  of  the  canals  and 
prevent  a  broach  gliding  into  them.  These  also  occur,  occa- 
sionally, within  the  canals,  partially  blocking  the  way  of  the 
broach.       Sometimes    the    pulp    chamber   will    be    filled    with 


130  PULP    CHAMBERS    OF    THE    DECIDUOUS    TEETH. 

nodular  deposits  so  completely  that  there  seems  to  be  no  room 
for  the  tissues  of  the  pulp.  These  deposits  will  have  to  be  re- 
moved before  the  root  canals  can  be  reached  and  entered, 
after  which  the  canals  will  generally  be  found  open.  These  de- 
posits occur  within  the  pulp  chambers  of  any  of  the  teeth ;  but 
they  cause  annoyance  more  frequently  in  the  molars. 

184.  Occasionally  lateral  openings  occur  from  the 
root  canals  to  the  surface  of  the  root.  I  have  seen  more  of 
these  from  the  canals  of  the  lower  molars  than  from  those  of 
any  other  teeth.  Generally,  they  follow  the  course  of  the  den- 
tal tubules,  and  open  on  the  side  of  the  root.  They  may  di- 
verge to  one  side  and  curve  toward  the  apex  of  the  root. 
These  cannot  often  be  detected,  except  in  dissections  of  the 
root,  and  occur  so  rarely  they  may  be  ignored  in  practice. 

185.  Sometimes  the  horns  of  the  pulp  approach  ab- 
normally near  the  points  of  the  cusps  of  some  of  the  teeth,  as 
in  the  upper  first  bicuspids  and  in  the  mesio-buccal  cusp  of  the 
upper  first  molar.  Then  the  pulp  is  more  liable  to  exposure 
in  excavating  carious  cavities. 

PULP    CHAMBERS    OF    THE    DECIDUOUS    TEETH. 

186.  The  pulp  chambers  of  the  deciduous  teeth  are 
proportionately  larger,  and  the  thickness  of  their  walls  less, 
than  those  of  the  corresponding  permanent  teeth.  The  pulps 
are,  in  consequence,  exposed  with  much  less  penetration  of 
tooth  substance,  and,  therefore,  more  liable  to  exposure  from 
caries,  or  in  the  use  of  cutting  instruments.  The  root  canals 
are  generally  larger  than  in  the  permanent  teeth  of  the  same 
denomination,  but  are  of  the  same  general  form.  Also,  the 
same  rules  for  finding  the  root  canals  in  the  permanent  molars 
apply  to  the  deciduous. 

ARRANGEMENT   OF    THE    TEETH. 

187.  The  upper  teeth  are  arranged  in  the  form  of  a 
semi-ellipse,  the  long  axis  passing  between  the  central  inci- 
sors (Figs.  126  and  127).     In  this  curve  the  cuspids  stand  a 


ARRANGEMENT     OF     THE    TEETH.  131 

little  prominent,  giving  a  fullness  to  the  corners  of  the  mouth. 
In  different  persons  there  is  much  variation  of  the  form  of  the 
arch  within  the  limits  of  the  normal.  Occasionally  the  bicus- 
pids and  molars  form  a  straight  line,  instead  of  a  curve,  and 
frequently  the  third  molars  are  a  little  outside  the  line  of  the 
ellipse.  In  the  examination  of  casts  of  the  most  perfect  den- 
tures it  is  found  that  the  two  sides  do  not  perfectly  correspond, 
and  that  certain  teeth  deviate  slightly  from  the  perfect  line. 
The  incisors  are  arranged  with  their  cutting  edges  forming  a 
continuous  curved  line  from  cuspid  to  cuspid,  and  this  line  is 
continued  over  the  cusps  of  the  cuspids  and  the  buccal  cusps 
of  the  bicuspids  and  molars  to  the  distal  surface  of  the  third 
molars.  From  the  first  bicuspid  to  the  third  molar  the  lingual 
cusps  of  these  teeth  form  a  second  line  of  elevations.  Between 
these  two,  the  lingual  and  buccal  cusps,  there  is  a  continuous, 
but  irregular,  valley  or  sulcus. 

188.  The  lower  teeth  are  arranged  similarly  (Fig.  185), 
but  on  a  slightly  smaller  curve,  so  that  the  line  of  the  ellipse, 
which  falls  on  the  buccal  cusps  of  the  upper  bicuspids  and 
molars,  will  fall  upon  the  buccal  surfaces  near  the  gum  on  the 
lower  teeth  (Fig.  126).  Therefore,  in  occlusion,  the  upper  teeth 
project  a  little  to  the  labial  and  buccal  of  the  lower  at  all  points 
of  the  arch  (Fig.  131).  The  incisors  and  cuspids  occlude  so 
that  the  cutting  edges  of  the  lower  incisors  and  cusps  of  the 
cuspids  make  contact  with  the  lingual  surfaces  of  the  similar 
teeth  of  the  upper  jaw  near  their  cutting  edges  (Fig.  128).  In 
this,  however,  there  is  much  variety  within  the  limits  of  a 
normal  occlusion.  Sometimes  the  lower  incisors  strike  the 
lingual  surfaces  of  the  upper  near  the  linguo-gingival  ridge, 
and  may  strike  at  any  point  between  that  and  the  cutting 
edges.  In  abnormal  occlusions  the  lower  incisors  may 
miss  the  upper,  striking  the  gums  posterior  to  them,  or  they 
may  occlude  anterior  to  the  upper  incisors.  The  broad- 
cusped  occlusal  surfaces  of  the  bicuspids  and  molars  of  the 
opposing  dentures  rest  on  each  other  in  such  a  way  that 
the   lingual  cusps  of  the   upper  teeth  fit  with   more   or   less 


132  ARRANGEMENT     OF     THE    TEETH. 


accuracy  into  the  general  sulcus  formed  between  the  buccal 
and  lingual  cusps  of  the  lower  teeth  The  buccal  row  of  cusps 
of  the  lower  teeth,  in  a  similar  way,  are  fitted  into  the  sulcus 
formed  between  the  buccal  and  lingual  cusps  of  the  upper  teeth 
(Figs.  129  and  130).  This  arrangement  is  such  that  when  the 
teeth  are  in  occlusion,  it  leaves  the  buccal  inclines  of  the  buccal 
'cusps  of  the  upper  teeth  outside  the  buccal  surface  of  the  lower 
teeth  (a),  and,  also,  leaves  a  ledge  formed  by  the  abrupt  lin- 
gual inclines  of  the  lingual  cusps  of  the  lower  teeth  along  the 
lingual  line  of  the  occlusion  (b).  This  brings  the  occlusal  sur- 
faces of  the  teeth  in  the  best  form  of  apposition  for  the  pur- 
poses of  mastication.  The  forms  presented  to  the  cheek  and 
to  the  tongue  hold  these  soft  tissues  a  little  apart  from  the 
actual  contact-points  of  the  occlusion,  and  thus  prevent  thera 
from  being  caught  and  pinched,  or  crushed,  between  the  teeth 
in  the  act  of  mastication.  In  youth,  while  the  permanent  teeth 
are  taking  their  places,  and  before  the  cusps  are  properly  fitted 
to  the  sulci,  we  often  find  the  cheeks  or  tongue  wounded  by 
being  caught  between  falsely  occluded  points.  With  the  after 
movements  of  the  teeth,  by  which  they  are  more  perfectly 
arranged,  this  difficulty  disappears. 

189.  The  line  from  before  backward  on  which  the  oc- 
clusion occurs  is  not  quite  a  plane;  in  the  lower  jaw  it  pre- 
sents a  slight  curve,  or  concavity,  and  in  the  upper  jaw  a  con- 
vexity (Fig.  131,  c  to  d).  This  concavity  of  the  line  of  the 
occlusal  surfaces  of  the  lower  teeth  is  a  little  greater  than  the 
convexity  of  the  upper,  so  that  the  cutting  edges  of  the  lower 
incisors  pass  a  little  beyond,  and  to  the  lingual  of  the  cutting 
edges  of  the  upper  incisors. 

190.  In  the  occlusion  the  relative  mesio-distal  position 
of  the  particular  teeth  of  the  upper  jaw  to  the  lower  is  im- 
portant (Fig.  131).  At  their  cutting  edges,  the  upper  central 
incisors  are  about  one-third  wider  mesio-distally  than  the 
lower  centrals.  The  upper  central,  therefore,  occludes  with 
the  lower  central,  and  also  with  from  one-third  to  one-half 
of  the  lower  lateral  incisor.     The  upper  lateral  occludes  with 


Fig.  126. 


Fig.  126  (Par.  187).— The  Elliptical  Form  of  the  Arch.  The  crowns  of  the 
teeth  of  both  upper  and  lower  jaws,  drawn  from  the  casts  of  a  very  regularly 
formed  arch,  and  the  line  of  a  true  ellipse  (in  dots)  placed  over  them,  showing  the 
comparative  size  of  the  upper  and  lower  arch,  and  the  deviations  from  perfect 
regularity. 


ARRANGEMENT   OF   THE   TEETH.  1 35 

the  remaining  portion  of  the  lower  lateral  and  the  mesial 
portion  of  the  lower  cuspid.  The  upper  cuspid  is  usually 
rather  broader  mesio-distally  than  the  lower,  and  in  occlu- 
sion covers  its  distal  two-thirds  and  about  half  of  the  lower 
first  bicuspid,  so  that  its  lingual,  or  triangular  ridge,  is  be- 
tween the  cusp  of  the  lower  cuspid  and  the  buccal  cusp  of 
the  lower  first  bicuspid,  the  point  of  its  cusp  overlapping 
the  lower  teeth.  The  buccal  cusp  of  the  lower  first  bicuspid 
occludes  in  the  space  between  the  upper  cuspid  and  upper 
first  bicuspid.  This  order  is  now  maintained  between  the 
bicuspids.  The  buccal  cusp  of  the  upper  first  bicuspid  over- 
laps (to  the  buccal)  the  space  between  the  two  lower  bicus- 
pids, and  its  lingual  cusp  occludes  in  the  sulcus  between  them, 
while  the  buccal  cusp  of  the  lower  second  bicuspid  occludes 
in  the  sulcus  between  the  two  upper  bicuspids.  The  cusps 
of  the  upper  second  bicuspid  occlude  between  the  lower 
second  bicuspid  and  lower  first  molar.  The  broad  surfaces 
of  the  molars  come  together,  so  that  the  mesial  two-thirds  of 
the  upper  first  molar  covers  the  distal  two-thirds  of  the  lower 
first  molar,  and  the  distal  third  of  the  upper  first  molar  covers 
the  mesial  third  of  the  lower  second  molar.  This  brings  the 
oblique  ridge  of  the  upper  molar  between  these  two  lower 
teeth.  This  order  is  continued  between  the  remaining  molars, 
but  less  perfectly  as  the  teeth  are  more  irregularly  formed. 
The  upper  third  molar  is  usually  smaller  than  the  lower  third 
molar,  yet  it  generally  extends  over  its  distal  surface. 

191.  The  inclination  of  the  teeth  is  the  deviation  of 
their  long  axes  from  the  perpendicular  line.  The  direction 
of  the  inclination  is  expressed  by  some  accompanying  word. 
The  upper  incisors  and  cuspids  are  so  arranged  that  their 
'crowns  are  inclined  more  or  less  forward,  or  toward  the  lip, 
and  slightly  toward  the  median  line.  The  mesial  inclination 
is  continued  in  the  bicuspids  and  molars,  diminishing  from 
before  backward,  and  is  usually  lost  at  the  second  or  third 
molar.  As  a  rule,  the  bicuspids  and  molars  of  the  upper  jaw 
are  also  slightly  inclined  toward  the  cheek,  but  in  many  den- 


136  ARRANGEMENT   OF   THE  TEETH. 

tures  this  inclination  is  slight,  or  wanting  in  the  bicuspids  and 
first  molars  to  reappear  in  the  second  and  third  molars,  though 
it  may  be  absent  even  in  these  without  necessary  malforma- 
tion. 

192.  The  lower  incisors  and  cuspids  are  also  inclined 
with  their  crowns  toward  the  lip,  but  in  less  degree  than  the 
upper.  And  even  the  perpendicular  position  of  these  is  not 
inconsistent  with  a  normal  arrangement.  They  have,  how- 
ever, a  mesial  inclination,  but  usually  much  less  than  the 
corresponding  upper  teeth.  The  lower  bicuspids,  within 
the  limits  of  the  normal  arrangement,  vary  considerably  in 
their  inclinations.  Sometimes  they  have  a  strong  mesial 
inclination,  and  at  other  times  they  are  nearly  or  quite  per- 
pendicular. In  many  dentures,  they  also  have  a  lingual  inclina- 
tion, but  may  be  perpendicular  or  even  have  a  slight  buccal 
inclination.  The  lower  molars  usually  have  a  slight  mesial 
and  lingual  inclination  (Fig.  135).  In  many  examples,  how- 
ever, the  mesial  inclination  is  wanting,  especially  in  the  second 
and  third  molars. 

193.  All  the  teeth  are  a  little  broader  mesio-distally  at 
or  near  the  occlusal  surfaces  than  at  their  necks.  Therefore, 
when  arranged  in  the  arch  with  their  proximate  surfaces  in 
contact,  there  is  a  considerable  space  between  their  necks 
(Fig.  131).  These  are  known  as  the  inter-proximate  or  V- 
shaped  spaces.  The  sharp  angle  or  apex  of  the  V-form  is 
toward  the  occlusal  surface,  or  at  the  contact-point  of  the 
proximation,  and  the  open  end  or  base  is  at  the  crest  of  the 
alveolar  process  (Figs.  134,  135,  136).  In  normal  conditions, 
this  space  is  filled  by  the  soft  tissues,  or  gums  (141).  The 
average  arch  measures  about  127  millimeters  (5  inches)  from 
the  distal  surface  of  the  right  third  molar  to  the  distal  surface 
of  the  left  third  molar,  following  the  curve  of  the  arch,  on  the 
line  of  the  contact-points  of  the  teeth.  This  represents  the 
average  mesio-distal  measurement  of  the  crowns  of  the  teeth 
of  the  upper  jaw  taken  collectively.  The  average  measure- 
ment of  the  teeth  at  their  necks  is  about  89  millimeters   (3.5 


Fig.  127. 


Fig.  128. 


Fig.  127*-  (Par.  1S7).— Arrangement  of  the  Teeth  in  the  Arch.  Tlie  arch  of 
the  .  upper   jaw. 

(Par.  210).— The  Teeth  and  the  Gums  and  the  Rug^  of  the  Roof  of  the 
Mouth. 

Fig.  128  (Par.  1S8).— Labio-Lingual  Position  of  the  Incisors  in  Occlusion. 

Fig.  129  (Par.  18S).— Bucco-Lingual  Position  of  the  Bicuspids  in  Occlu- 
sion. 

Fig.  130  (Par.  188).— Bucco-Lingual  Position  of  the  Molars  in  Occlusion. 


'Illustration,   actual  size. 


ARRANGEMENT   OF    THE   TEETH.  I39 

inches).  The  remaining  38  millimeters  (1.5  inches)  represent 
the  average  sum  of  the  inter-proximate  spaces  taken  col- 
lectively. 

194.  On  account  of  differences  in  the  conformation  of 
the  crowns  and  the  inclination  of  the  teeth  the  inter- 
proximate  spaces  vary  much  in  width  in  different  dentures. 
They  are  much  wider  between  bell-crowned  teeth  than  be- 
tween thick-necked  teeth;  but  some  inter-proximate  space 
exists  in  every  normal  denture.  When  the  crowns  of  the 
incisors  and  cuspids  are  much  inclined  toward  the  lip,  the 
necks  of  the  teeth  form  a  smaller  circle  than  the  line  of  the 
contact-points  of  the  proximation,  and  in  this  way  the  inter- 
proximate  spaces  may  be  considerably  narrowed.  Generally, 
the  inter-proximate  space  is  wide  between  the  necks  of  the 
central  incisors.  The  suture  joining  the  maxillary  bones 
passes  between  the  roots  of  these  teeth,  and  they  are  somewhat 
farther  apart  than  the  roots  of  the  central  and  lateral  incisors, 
or  those  of  the  lateral  incisor  and  the  cuspid.  Therefore,  in 
these  latter,  the  inter-proximate  spaces  are  of  less  width  (Fig. 
134).  Between  the  bicuspids  the  inter-proximate  spaces  are 
wider  at  the  necks  of  the  teeth  than  between  the  anterior 
teeth,  on  account  of  the  greater  breadth  of  the  crowns  as 
compared  with  the  roots  (Fig.  135,  b).  The  widest  inter- 
proximate  spaces  are  usually  between  the  necks  of  the  molars 
(Figs.  135  and  136,  c). 

When  the  proximate  surfaces  of  the  teeth  are  carefully 
examined  it  is  found  that  at  the  level  of  the  contact-point  they 
are  more  or  less  rounded  from  buccal  to  lingual,  and  in  this 
rounding  the  mesio-distal  diameter  of  the  bicuspids  and 
molars  is  narrowed  more  toward  the  lingual  than  toward  the 
buccal.  This  gives  rise  to  spaces  between  the  angles  of  the 
teeth,  which  begin  at  the  point  of  proximate  contact  and  widen 
toward  the  buccal  on  the  one  side  and. toward  the  lingual  upon 
the  other.  These  are  the  buccal  and  lingual  inter-proximate 
embrasures  (see  Figs.  132  and  133).  The  depth  of  these 
embrasures  and  their  width  vary  greatly  in  different  den- 
tures.     Usually    between   bell-crowned    teeth    they    are    deep. 


140  ARRANGEMENT   OF   THE   TEETH. 

while  between  thick-necked  teeth  they  are  shallower.  The 
lingual  embrasures  are  generally  much  deeper  than  the  buccal 
between  the  angles  of  the  bicuspids  and  molars,  while  the 
labial  embrasures  are  deeper  than  the  lingual  between  the 
angles  of  the  incisors. 

The  form  of  these  inter-proximate  embrasures  seems  to 
be  important  with  reference  to  cleanliness  of  the  inter-proxi- 
mate spaces ;  for  when  they  are  deep,  food,  in  its  excursions 
over  the  teeth  and  gums  during  mastication,  is  directed  into 
them,  and  is  caused  to  glide  out  to  the  lingual  and  to  the 
buccal,  rubbing  through  the  embrasures  and  over  the  gum 
septum  and  carrying  away  all  debris  that  may  have  found 
lodgment  about  the  inter-proximate  spaces. 

195.  The  points  of  proximate  contact  in  the  best- 
formed  arches  are  near  the  occlusal  surfaces  of  the  teeth.  In 
imperfectly  developed  teeth,  in  which  the  crowns  are  much 
rounded  toward  the  occlusal  surfaces,  the  contact  points  are 
more  toward  the  gingival.  In  the  incisors  and  cuspids  they 
are  in  direct  line  with  the  cutting  edges  (Fig.  132,  a).  In  the 
bicuspids  the  contact  is  near  the  mesio-  and  disto-bucco- 
occlusal  angles  and  nearly  in  line  with  buccal  cusps  (Fig. 
132,  b).  The  mesial  and  distal  Battened  surfaces  of  these  teeth 
converge  to  the  lingual  to  such  an  extent  that,  though  they  are 
arranged  in  arch  form  the  contact-points  remain  close  to  the 
buccal-point  angles.  In  many  excellent  dentures  there  is  a 
decided  interproximate  embrasure  opening  to  the  lingual 
but  in  thick-necked  teeth  and  those  of  a  more  rounded  con- 
tour, the  contact-points  are  often  more  toward  the  lingual,  and 
there  is  but  a  slight  lingual  embrasure.  In  thfe  molars  the 
contact-points,  as  a  rule,  are  removed  rather  more  to  the 
lingual,  but  still  in  the  best-formed  dentures  they  will  be  found 
nearly  in  line  with  the  buccal  cusps  (Fig.  132,  c).  Between 
the  upper  first  and  second  molars  the  contact-point  is  often 
extended  toward  the  lingual  by  the  prominent  disto-lingual 
cusp  of  the  first  molar ;  and,  even  when  otherwise,  the  general 
rounding   of   the   distal   surfaces   of   the   upper   molars   often 


i--i---:- 


...v 

ma 


\ 


Fig.  131. — Actual  size. 


Fig.  131  (Par.  188). — Arrangement  of  the  Teeth.  Labial  and  buccal  aspect  of 
the  upper  and  lower  teeth   as   arranged   in   the   arch. 

(Par.  197). — The  Alveolar  Process  of  the  Upper  and  Lower  Jaws,  with 
THE   Teeth    in    Position. 


ARRANGEMENT    OF    THE    TEETH.  I43 

brings  the  contact-point  near  the  middle  line  of  the  teeth. 
In  lower  first  molars  the  large  distal  cusp  brings  the  contact- 
point  with  the  second  molar  close  to  the  buccal  side,  with  a 
considerable  lingual  inter-proximate  embrasure  (Fig.  133,  c). 
If  the  distal  cusp  is  small,  the  contact-point  is  usually  extended 
toward  the  lingual,  often  as  far  as  half  the  bucco-lingual 
breadth  of  the  teeth.  Between  the  second  and  third  molars 
the  contact-point  is  most  frequently  near  the  central  line  of 
the  teeth  (Fig  133,  d).  In  the  best-formed  dentures  the 
form  of  the  proximate  contact  is  such  as  to  prevent  food 
from  being  crowded  between  the  teeth  in  mastication,  and 
therefore,  such  as  to  keep  these  spaces  clean  and  the  inter- 
proximate  gingivae  in  health.  But  many  faulty  forms  are 
met  with  which  allow  food  to  leak  through  into  the  inter- 
proximate  space  and  crowd  the  gum  away,  forming  a  pocket 
for  the  lodgment  of  debris,  giving  opportunity  for  decom- 
position, and  resulting  in  caries  of  the  proximate  surfaces,  or 
disease  of  the  gum  and  peridental  membrane.  A  close  study 
of  the  forms  of  proximate  contact  in  the  best-formed  dentures 
demonstrate  that  the  immediate  contact-point  is  on  rounded 
prominences  of  the  proximate  surfaces.  The  rounding  of  the 
surfaces  bucco-lingually  and  the  form  of  the  buccal  and  lingual 
inter-proximate  embrasures  are  well  shown  in  Figs.  132,  133, 
which  were  made  by  removing  the  occlusal  surfaces  of  the 
teeth  by  grinding  until  the  contact-points  were  reached,  and 
then  accurately  drawing  the  outlines  to  show  the  form  of  the 
contact-points.  In  Figs.  134,  135,  and  136  the  outlines  of  the 
teeth  are  carefully  drawn,  so  as  to  illustrate  the  form  of  the 
contact  occluso-gingivally,  from  which  it  will  be  seen  tha-t 
they  are  sharply  rounded  in  this  direction  also.  Therefore 
the  proximate  contact  of  the  teeth  is  such  as  would  be  made 
by  the  contact  of  two  marbles,  or  at  a  single  small  point. 
These  points  of  proximate  contact  also  slide  slightly  upon 
each  other  in  the  act  of  chewing  food,  the  peridental  mem- 
branes allowing  the  teeth  a  slight  motion,  so  that  any  sub- 
stance forced  between  them  easily  glides  out  in  one  way  or 

II 


144         '^HE  ALVEOLAR  PROCESS  AND  ALVEOLI. 

the  Other.  Furthermore,  the  form  of  the  inter-proximate 
gum  tissue,  the  gum  septum,  is  that  of  an  arch  with  its  con- 
vex side  toward  the  point  of  contact  or  occlusal  surfaces  of 
the  teeth.  Therefore,  food-material  forced  past  the  rounded 
point  of  contact,  and  lying  loosely  in  the  inter-proximate 
space,  and  upon  this  rounded  and  tolerably  firm  gum  septum, 
is  caught  and  carried  away  by  the  gliding  motion  of  food 
over  the  axial  surfaces  of  the  teeth  and  over  the  gum  tissue 
in  the  act  of  chewing.  This  is  facilitated  greatly  by  wide 
buccal  and  lingual  inter-proximate  embrasures,  which  allow 
the  food  to  glide  through  them  during  mastication.  In  this 
way  the  proximate  surfaces  of  normally  well-formed  teeth  are 
kept  free  from  lodgments  as  long  as  the  gum  septum  retains 
its  normal  form  and  firmness.  In  many  individuals  of  middle, 
or  advanced  age,  the  points  of  proximate  contact  become 
much  worn  and  flattened  by  rubbing  on  each  other  during 
mastication.  From  this  cause  they  often  become  so  broad  as 
to  hold  food-material  firmly  between  them,  which  is  gradually 
forced  against  the  gum  septum,  causing  its  absorption,  and 
forming  a  pocket  for  the  lodgment  of  debris,  and  thus  gives 
rise  to  serious  difficulties.  Facets  formed  by  inter-proximate 
wear  may  be  found  in  any  collection  of  teeth.  Exceptionally 
cases  are  met  with  in  which  the  teeth  stand  so  widely  apart 
that  they  are  self-cleaning.  The  form  of  the  inter-proximate 
space  is  very  variable.  The  forms  best  suited  to  the  mainte- 
nance of  the  health  of  the  teeth  and  gums  are  so  important  to 
the  student  of  operative  dentistry  that  they  should  be  very 
closely  studied.  It  is  best  studied  in  skulls  in  which  the  teeth 
are  all  present,  by  careful  selection  and  arrangement  of  teeth 
with  their  roots  in  wax,  gutta-percha,  or  plaster,  to  hold  them 
in  normal  relation  to  each  other,  and  by  careful  consideration 
of  the  forms  of  the  proximate  surfaces  of  the  teeth  together 
with  their  relative  positions. 

THE  ALVEOLAR  PROCESS  AND  ALVEOLL 

■ —      196.     The   alveolar    process   is   the   projecting   portion 
of  the  maxillarv  bones  within  which   the  roots  of  the   teeth 


ngm^BUM 


Fig.  135.  Fig.  136. 

Fig.  132  (Pars.  19.1,  195). — The  Form  of  the  Inter-Pkoximate  Contact  from 
Buccal  to  Lingual  of  the  Upper  Teeth.  The  occlusal  surfaces  of  the  teeth  are 
ground  away  vmtil  the  contact-points  are  reached,  and  then  the  outlines  are  accu- 
rately drawn  in  silhouette,     a,  Incisors;  b,  bicuspids;  c,  molars. 

Fig.  133  (Pars.  194,  195).— The  Form,  Bucco-Lingually  of  the  Inter-Proxi- 
mate Contact  of  the  Lower  Molars  and  Bicuspids.  The  occlusal  surfaces  of 
the  teeth  are  ground  away  until  the  contact-points  were  reached  and  the  outlines 
accurately  drawn  in  silhouette,  a,  Contact  of  th^  bicuspids;  b,  contact  of  the  sec- 
ond bicuspid  and  first  molar;  c,  contact  of  the  first  and  second  molars;  d,  contact 
of  the  second  and  third  molars. 

Fig.  134  (Pars.  194,  19s). — The  Form,  Occluso-Gingivally,  of  the  Inter- 
Proximate  Contact  and  of  the  Inter-proximate  Spaces  between  the  Upper 
Incisors,     a,   Alveolar  process. 

Fig.  135  (Pars.  194,  195). — The  Form,  Occluso-Gingivally,  of  the  Inter- 
Proximate  Contact  and  of  the  Inter-proximate  Spaces  between  the  Bicus- 
pids and  Molars  of  the  Upper  Jaw.  a,  Alveolar  process;  b,  bicuspids;  r, 
molars. 

Fig.  136  (Pars.  194,  195).— The  Form,  Occluso-Gingivally,  of  the  Inter- 
Proximate  Contact  and  of  the  Inter-proximate  Spaces  between  the  Lower 
Bicuspids  and    Molars,     a.  Alveolar   process;  b,  bicuspids;   r,   molars. 


THE    ALVEOLAR    PROCESS    AND    ALVEOLI.  147 

are  lodged  in  alveoli,  or  sockets,  accurately  fitted  to  their 
surfaces  (Figs.  137  and  138).  The  form  of  the  alveolar 
process  seems  to  depend  on  the  teeth,  the  conformation  of 
their  roots,  and  their  arrangement  in  the  arch.  If  any  teeth 
are  misplaced,  or  from  any  cause  stand  out  of  the  regular  and 
normal  line,  the  alveolar  process  is  formed  about  their  roots  in 
this  irregular  position.  Also,  when  teeth  are  lost,  the  alveolar 
process  mostly  disappears  by  absorption,  and  the  remaining 
portions  of  the  alveoli  are  filled  with  bone. 

197.  Normally,  the  alveolar  process  envelopes  the  roots 
of  the  teeth  to  within  a  short  distance  of  the  gingival  line 
(Figs.  131  and  139),  varying  from  one  to  three  millimeters  in 
the  young  adult.  This  distance  increases  somewhat  with  in- 
creasing age.  The  borders  of  the  alveolar  process  are  reduced 
to  a  thin  edge  about  the  necks  of  the  teeth  on  both  the  labial 
and  lingual  sides  of  the  incisors  and  cuspids  of  the  upper  jaw. 
About  the  lingual  sides  of  the  necks  of  the  bicuspids  and  mo- 
lars the  borders  are  also  reduced  to  a  thin  edge,  becoming 
slightly  thickened  about  the  second  and  third  molars,  especi- 
ally the  latter.  On  the  buccal  sides  of  these,  a  thickening  of 
the  immediate  borders  of  the  alveolar  process,  in  the  form  of  a 
marked  ridge,  begins  about  the  first  or  second  bicuspid,  more 
commonly  between  these  two,  and  extends  to  the  distal  of  the 
third  molar  (Fig.  131,  a).  This  ridge  varies  in  different  exam- 
ples, from  a  very  slight  thickening  of  the  immediate  border  to 
a  thickness  of  two  or  three  millimeters.  It  forms  a  border 
standing  squarely  out  from  the  necks  of  the  teeth.  The  alveo- 
lar process  then  thins  away  so  that,  in  many  instances,  the  buc- 
cal roots  of  the  teeth,  especially  the  mesial  root  of  the  first 
molar,  have  but  a  thin  covering  of  bone. 

198.  Anteriorly,  the  bony  covering  of  the  roots  of  the 
upper  incisors  presents  much  variety.  In  some  examples,  the 
middle  portion  of  the  roots  has  but  a  slight  covering  of  bone, 
but  more  generally  it  is  progressively  thickened  from  the  neck 
to  the  apex.  The  roots  of  the  cuspids  are  prominent  toward 
the  lip,  and,  for  most  of  their  length,  have  only  a  thin  bony 


148  THE    ALVEOLAR    PROCESS    AND    ALVEOLI. 

covering,  and  this  forms  a  ridge  along  the  hne  of  the  root, 
which  mav  easily  be  traced  with  the  finger  through  the  soft 
tissues  of  both  the  gum  and  lip.  In  many  instances,  the  bony 
covering  is  entirely  wanting  for  a  little  space  near  the  middle 
of  the  length  of  the  root  of  the  cuspid,  the  buccal  root  of  the 
first  bicuspid,  the  mesial  root  of  the  first  molar,  and,  occasion- 
ally, of  other  teeth. 

199.  On  the  lingual  side  of  the  upper  teeth  (Fig.  139) 
the  progressive  thickening  of  the  alveolar  process,  from  the 
border  toward  the  apex  of  the  root,  is  much  greater,  so  that 
the  roots  of  the  teeth  seem  to  lie  toward  the  labial  and  buccal 
side  of  the  alveolar  process  (Fig.  137).  Even  the  large  lingual 
root  of  the  upper  first  molar,  diverging  strongly  to  the  lingual, 
seldom  forms  a  ridge  or  prominence  of  the  process  covering 
its  lingual  surface. 

200.  The  anterior  palatine  foramen  is  in  the  median 
line  just  behind  the  central  incisors  (Fig.  139).  It  is  funnel- 
shaped,  with  a  broad  opening  to  the  palatine  surface  of  the 
bone.  The  bone  is  often  quite  thin  between  this  and  the  roots 
of  the  central  incisors.  The  posterior  palatine  artery  runs 
in  a  deep  groove  in  the  surface  of  the  bone,  very  close  to  the 
apex  of  the  lingual  roots  of  the  upper  third  and  the  upper 
second  molar.  This  artery  is  occasionally  wounded,  or  cut, 
in  efforts  to  extract  the  roots  of  these  teeth. 

201.  In  the  lower  jaw  the  immediate  borders  of  the 
alveolar  process,  on  the  labial  sides  of  the  incisors,  are  rather 
thicker  than  in  the  upper  jaw,  often  amounting  to  a  decided 
ridge.  This,  however,  thins  away  rapidly,  so  that  the  middle 
portion  of  the  root  has  but  a  thin  covering  of  bone.  At  the 
cuspid  the  border  of  the  alveolar  process  is  very  thin,  but  a 
gingival  ridge,  corresponding  with  that  of  the  upper  jaw, 
though  not  so  prominent,  begins  at  about  the  first  or  second 
bicuspid  and  runs  to  the  second  molar.  This  thins  away  over 
the  middle  of  the  length  of  the  roots  of  the  bicuspids  and  first 
molar.  At  the  second  lower  molar,  the  rising  of  the  external 
oblique  ridge  for  the  formation  of  the  anterior  border  of  the 


Fig.  137- 


Fig.  138. 


Fig.  139. 


Fig.  137*  (Par.  196).— Horizontal  Section  of  the  Alveolar  Process  and 
Roots  of  the  Teeth  of  the  Upper  Jaw,  showing  the  roots  of  the  teeth  in  posi- 
tion. 

Fig.  138*  (Par.  196). — Horizontal  Section  of  the  Alveolar  Process  and 
Roots  of  the  Teeth  of  the  Lower  Jaw,  showing  the  roots  of  the  teeth  in  posi- 
tion. 

Fig.  139*  (Par.  197). ^The  Teeth  and  Lingual  Portion  of  the  Alveolar 
Process  of  the  Upper  Jaw,  and  the  Bones  of  the  Roof  of  the  Mouth. 


^Illustration,    actual    size. 


THE    ALVEOLAR    PROCESS    AND    ALVEOLI.  15T 

coronoid  process  (Fig.  131,  b)  causes  a  thickening  of  the  buc- 
cal bony  covering  of  the  root,  while  at  the  third  molar  this 
ridge  rises  to  a  level  with  the  border  of  the  alveolar  process, 
making  the  bony  covering  on  the  buccal  side  of  the  root  about 
one-fourth  of  an  inch  thick  (Fig.  138).  This  is  of  importance 
with  reference  to  the  extraction  of  the  roots  of  this  tooth.  In- 
deed, the  second  and  third  molars  of  the  lower  jaw  are  fixed  in 
alveoli,  hollowed  out  in  the  lingual  side  of  the  body  of  the 
bone  rather  than  in  a  process  or  ridge  on  the  bone,  as  with 
the  teeth  anterior. 

202.  On  the  lingual  side  of  the  lower  anterior  teeth 
the  border  of  the  alveolar  process  is  a  smooth,  thin  edge,  and 
the  covering  of  bone  over  the  roots  progressivelv  thickens 
toward  their  apexes.  In  this  portion  the  process  is  high,  and 
the  labio-lingual  thickness  is  only  sufficient  to  envelope  the 
roots  of  the  teeth  and  give  them  support  (Figs.  140  and  142). 
From  the  first  bicuspid  backward  the  height  of  the  alveolar 
process  diminishes  rapidly,  and  the  line  of  the  dental  arch  and 
of  the  alveoli  of  the  teeth  passes  diagonally  across  the  line  of 
the  curve  of  the  body  of  the  bone,  from  the  buccal  side  at  the 
first  bicuspid  to  the  lingual  side  at  the  third  molar,  and  sinks 
into  the  body  of  the  bone  (Figs.  140  and  142).  The  border  of 
the  alveolar  process  remains  thin  as  far  as  the  first  or  second 
molar,  but  the  bony  covering  of  the  roots  is  rapidly  thickened 
toward  their  apexes. 

203.  This  is  caused  largely  by  the  thickening  of  the  body 
of  the  bone,  produced  by  the  rise  of  the  mylohyoid  ridge 
(Fig.  142,  a),  which  begins  in  front  below  the  apexes  of  the 
roots  and  rises  progressively  backward  nearly  to  the  border  of 
the  alveolar  process  at  the  third  molar.  The  greatest  thickness 
is  oyer  the  lingual  side  of  the  apical  half  of  the  roots  of  the  sec- 
ond molar,  and  of  the  crossing  of  the  lingual  side  of  the 
coronal  half  of  the  roots  of  the  third  molar.  At  the  third  molar 
this  ridge  is  thinner,  and  at  the  distal  angle  often  very  slight, 
while  the  lingual  covering  of  the  roots  of  the  tooth  may  be 
verv  thin  below  this  ridge.    Therefore,  it  is  usually  easy,  when 


152  THE  PERIDENTAL  MEMBRANE. 


necessary  in  extracting,  to  force  the  roots  of  the  lower  third 
molar  to  the  lingual  and  distal  with  a  level  suitably  arranged 
against  the  crown  of  the  second  molar,  as  with  the  Physic's 
forceps,  or  an  elevator. 

204.  The  borders  of  the  septa  of  the  alveoli  of  the  roots 
of  the  anterior  teeth  are  rounded,  or  arched  labio-lingually, 
but  this  diminishes  rapidly  from  the  cuspid  backward.  Be- 
tween the  molars  it  is  a  straight  line,  or  presents  but  a  slight 
concavity,  so  that  the  highest  points  of  the  border  of  the 
alveolar  process  are  on  the  buccal  and  lingual  surfaces,  or  at 
the  angles,  of  the  necks  of  these  teeth,  which  is  important  in 
fitting  bands  of  crowns  or  any  similar  processes. 

205.  The  alveolar  process  is  composed  of  an  outer  and 
an  inner  plate  of  moderately  compact  bone,  and  between 
these,  very  open  cancellous  or  spongy  bone ;  so  that  in  young 
persons  it  may  be  forced  more  or  less  to  one  side,  or  bent  out 
of  position,  without  definite  fracture.  The  outer  compact  plate 
forms  the  outer  surface  of  the  bone,  and  the  inner  plates  line 
the  alveoli  of  the  teeth.  These  latter  are  very  thin,  and  sup- 
ported on  all  sides  by  the  cancellous  structure.  In  the  lower 
jaw  the  substance  of  the  bone  is  more  compact  and  stronger, 
than  in  the  upper,  especially  about  the  molar  teeth,  where  the 
alveoli  are  in  the  substance  of  the  body  of  the  bone. 

THE  PERIDENTAL  MEMBRANE. 

206.  The  peridental  membrane  invests  the  roots  of 
the  teeth  from  the  gingival  line  to  the  apexes  of  the  roots  like 
a  sack.  It  lines  every  part  of  the  alveoli,  and,  passing  over  the 
gingival  margins,  is  continuous  with  the  periosteum  and  gums 
covering  the  outer  plate  of  the  alveolar  process.  It  is  one 
membrane,  attached  on  one  side  to  the  root  of  the  tooth,  and 
on  the  other  to  the  inner  wall  of  the  alveolus.  It  is  composed 
of  connective  tissue  which  supports  an  abundant  supply  of 
blood-vessels,  nerves  and  lymphatics.  With  these  are  inter- 
mingled strong  fibres  of  white  fibrous  tissue  which  pass  from 
the  cementum  of  the  root  of  the  tooth  to  the  bony  walls  of  the 


Fig.  140. — Actual  size. 


Fig.  141. — Actual  size. 


Fig.   140   (Par.  202).^Lower  Teeth  and  Maxilla,  as  seen  from  above. 
Fig.   141     (Par.  210). — The     Labial  and    Buccal   Aspect    of    the    Teeth    and 
Gums   of   the  Upper   Jaw. 


THE    GUMS.  '  155 


■  alveolus.  The  ends  of  these  are  built  firmly  into  each,  forming 
a  strong  attachment  of  the  root  to  its  alveolus.  In  childhood 
and  youth,  this  membrane  is  comparatively  thick,  and  allows 
considerable  motion  of  the  tooth  in  its  socket.  As  age  ad- 
vances, it  becomes  thinner  and  the  motions  of  the  teeth  are 
more  restricted.  A  bundle  of  nerves  and  one  or  more  arteries 
enter  the  alveolus  near  the  apex  of  the  root  (the  apical  space), 
and,  subdividing,  several  arterial  twigs  and  nerve  bundles  pass 
toward  the  gingiva,  while  others  enter  the  apical  foramen  and 
pass  to  the  pulp  of  the  tooth.  Also,  the  cancellous  portion  of 
the  bone  forming  the  alveolar  process  is  richly  supplied  with 
blood-vessels  and  nerves,  and  these  enter  the  alveolus  and  peri- 
dental membrane  from  all  sides.  This  gives  the  peridental 
membrane  a  very  rich  collateral  circulation.  At  the  gingivae, 
the  blood-vessels  become  continuous  with  those  of  the  perios- 
teum and  gums.* 

THE  GUMS. 

207.  The  gums  are  the  soft  tissues  covering  the  alveolar 
-processes  and  investing  the  necks  of  the  teeth.  They  are  com- 
posed of  connective  tissue  containing  many  white  fibres 
intermingled,  forming  a  firm  membranous  mass,  continuous 
with  the  periosteum  beneath,  and  with  the  peridental  mem- 
brane at  the  necks  of  the  teeth.  They  are  covered  with  a 
strong  outer  coat  of  squamous  epithelium.  They  are  richly 
supplied  with  blood-vessels  and  nerves ;  under  normal  con- 
ditions they  are  not  very  sensitive  to  pressure  or  moderate 
violence,  but  in  pathological  conditions  they  may  become  very 
sensitive. 

208.  On  the  labial  and  buccal  side  of  the  alveolar  pro- 
cess the  gums  (Fig.  136)  are  thin  and  firm  near  the  necks  of 

the  teeth  and  strongly  attached  to  the  periosteum.  As  they 
pass  from  the  necks  of  the  teeth  toward  the  base  of  the  alveolar 
ridge  they  become  softer,  lose  their  close  attachment  to  the 

*  For  the  details  of  this  subject  the  student  is  referred  to  the 
author's  treatise  on  "The  Histological  Characters  of  the  Periosteum 
and  Peridental  Membrane." 


156  THE    GUMS. 


periosteum,  and  become  merged  into  the  mucous  membrane  of 
the  Hps  and  cheeks.  In  the  passage  from  the  gums  to  these 
mucous  surfaces  several  loose  folds  are  formed,  the  most  no- 
table being  the  frenum  labium  of  the  upper  jaw  at  the 
median  line,  passing  from  near  the  inter-proximate  space  of 
the  central  incisors  to  the  median  line  of  the  upper  lip.  A 
similar,  though  less  prominent  fold  connects  the  median  line 
of  the  lower  lip  with  the  gums.  Occasionally,  folds  of  less 
prominence  are  seen  in  the  neighborhood  of  the  bicuspids  and 
first  molars. 

209.  On  the  lingual  side  of  the  arch,  in  the  lower  jaw, 
the  conditions  are  much  the  same.  The  gums  are  firmly  ad- 
herent to  the  periosteum  near  the  teeth,  but  lower  down  are 
merged  into  the  mucous  membrane  of  the  floor  of  the  mouth. 
The  median  line  of  the  tongue  is  connected  with  the  median 
line  of  the  gums  by  a  strong  fold,  known  as  the  frenum  lin- 
guae. As  an  abnormal  congenital  condition  this  is  sometimes 
connected  so  near  the  tip  of  the  tongue  as  to  prevent  its  pro- 
trusion over  the  teeth,  constituting  the  condition  known  as 
tongue-tied.  This  is  generally  corrected  by  the  muscular 
efforts  of  the  tongue,  which  stretch  the  membrane  sufficiently 
to  accommodate  its  motions. 

210.  On  the  lingual  side,  in  the  upper  jaw,  the  gums 
(Fig.  127)  are  usually  of  greater  extent  and  thicker.  They 
cover  the  entire  roof  of  the  mouth,  to  the  conjunction  of  the 
hard  and  soft  palate,  as  a  hard  dense  layer.  In  the  anterior 
portion,  a  series  of  irregular  ridges,  known  as  the  rugae,  radi- 
ate from  the  median  line  toward  both  sides,  stopping  short  of 
the  gingivae.  In  a  large  collection  of  examples  almost  innu- 
merable forms  of  these  rugae  may  be  noted. 

211.  The  gingiva,  or  gingivae,  is  that  portion  of  the 
gum  tissue  investing  the  neck  of  the  tooth  crownwise  from  the 
attachment  of  the  peridental  membrane  at  the  gingival  line 
(Fig.  143).  It  is  also  termed  the  free  margin  of  the  gum^ 
The  length  of  the  gingivae,  from  the  line  of  attachment  to  the 
neck  of  the  tooth,  varies  in  different  teeth  in  the  same  mouth, 


Fig.  142. — Actual  size. 


Fig.  143- 


Fig.  142  (Par.  202). — Lingual  Surface  of  the  Left  Half  of  the  Lower 
Maxilla  and  Teeth,     a,  Myloiiyoid  ridge;  b,  inferior  dental  foramen. 

Fig.  143  (Par.  211). — Outlines  of  a  Section  of  a  Central  Incisor,  cut 
Lengthwise  Labio-Lingually,  with  its  alveolus  and  appendages  showing  the  re- 
lation of  the  different  parts,  a,  Crown  of  the  tooth;  b,  root;  c,  c,  bone;  d,  d, 
alveolar  process;  e,  c,  peridental  membrane;  f,  f,  gums;  g,  g,  gingivae,  or  free 
margin  of  the  gums;  /;,  gingival  line;  the  portions  of  the  crown  included  within  the 
dotted  lines  i  shows  the  portion  of  the  proximate  surfaces  covered  by  the  inter- 
proximate   gingivae    in    normal   conditions. 


THE    GUMS.  159 


and  in  different  adults,  from  about  one  to  about  four  millime- 
ters. It  is  often  much  greater  in  young  persons,  but  the  length 
usually  diminishes  as  age  advances.  The  free  margin  fits 
around  the  neck  of  the  tooth  closely,  but  a  thin,  flat  instrument 
is  easily  passed  between  it  and  the  tooth  to  the  attachment  at 
the  gingival  line.  As  the  gingival  line  of  the  tooth  is  at  the 
border  of  the  enamel,  or  at  the  junction  of  the  enamel  and 
cementum,  it  follows  that  the  gingivae  inclose  the  immediate 
gingival  border  of  the  enamel,  and  cover  this  part  of  the  crown 
of  the  tooth.  In  young  persons,  we  often  see  one-half  of  the 
length  of  the  crowns  of  the  teeth  buried  in  the  gingivae  even 
after  the  teeth  are  regarded  as  fully  in  place.  As  age  advances, 
the  gingivae  become  shorter,  showing  more  of  the  crown,  and 
finally  recede  to  very  near  the  gingival  line. 

212.  The  gingivae  also  fill  the  inter-proximate  spaces 
in  the  form  of  septa  passing  between  the  teeth  from  labial, 
or  buccal,  to  lingual.  This  portion  of  the  gingivae  is  much 
longer  than  that  on  the  labial  and  lingual  surfaces  of  the 
teeth  (Figs.  136  and  143).  In  normal  conditions  it  reaches 
from  the  gingival  line  to  the  contact-point  between  the  teeth, 
completely  filling  the  space  and  preventing  accumulations  of 
debris.  The  form  presented  by  the  gingivae  on  the  labial  and 
buccal  surfaces  is  a,  series  of  imperfect  semi-circles  with  the 
concavity  toward  the  occlusal  surfaces  of  the  teeth,  and  with 
the  points  of  junction  of  these  extending  into  and  filling  the 
inter-proximate  spaces  (Fig.  141).  On  the  lingual  side  of  the 
arch,  the  conditions  are  much  the  same,  but  the  points  of  the 
gingivae  between  the  teeth  are  less  prominent  (Fig.  27).  As 
age  advances  and  the  gingivae  recede  toward,  or  even  to  the 
gingival  line,  the  septa  of  soft  tissue  fail  to  fill  the  inter-proxi- 
mate spaces.  This  may  induce  pathological  conditions  by 
affording  space  for  lodgment  of  debris  in  pockets,  which 
favors  fermentation.  A  like  condition  is  also  induced  fre- 
quently by  a  faulty  form  of  proximate  contact,  or  through  the 
flattening  of  the  contact  points  by  wear,  which  allows  food  to 
be  forced  into  the  inter-proximate  space,  and  break  down  the 
gum  septum  by  its  pressure. 

12 


INDKX. 

'the  numbers  refer  to  the  paragraphs. 

Alveolar  process     196 

"              "      — at  the  buccal  side  of  the  lower  third  molar. .  201 

"              "      — bone  forming  the 205 

"              "      — borders  of 197 

"              "      — buccal  ridge  197 

"              "      — lower  labial  portion 201 

"              "                "       lingual  portion 202 

"              "       — relation  of  the  mylohyoid  ridge.   , 203 

"               "                "             "         oblique  ridge  201 

"              "      — septa  of  the 204 

"              "      — upper  labial  portion 198 

"              "               "        lingual   portion    199 

Alveoli    •  • 196 

"      — relation  of  the  roots  of  the  teeth 197 

Angles —  of  the  teeth,  how  named 7 

"              "       surfaces  of  the  teeth,  how  named 7 

Apical  foramen  153 

Apex  of  the  root  defined 3 

Arrangement  of  the  teeth 187 

Bell-crowned  teeth  14 

"            "            "    — inter-proximate    spaces 194 

Bicuspids    41 

"        — buccal  surface  of  the  lower  first 57 

"                "'              "          "            "      second    63 

"                "               "           "         upper  first   46 

"                "               "           "             "       second   52 

"        — distal  surface  of  the  lower  first 58 

"                "              "           '"'             "       second    64 

"                "               "           "         upper  first     49 

"                "■              '■'          "            "       second    52 

"        ^grooves  of  lower  first ^ . .  .     54.  55 

. "                "              "       '■       second    62 

"                "               '■'  upper  first    45 

"                "■             "       "       second    51 

"        — lingual  surface  of  the  lower  first 59 

'■       •         "                 "■           '■             "       second    63 

"                "                 "           "         upper  first     47 

"                '•■                "          "            "       second    52 

161 


I 62  INDEX. 


Bicuspids — mesial  surface  of  the  lower  first 58 

"              "          "            "       second   64 

"               "           '■         upper  first   48 

"              "          "            "       second    52 

— occlusal  surface  of  lower  first 54 

"                ■'           "         '■       second     62 

"                "           "     upper  first   42 

"               "          "         "       second    Si 

— plan  of  the  formation 41 

— root  of  lower  first 61 

"       "       "      second    65 

"      "  upper  first    50 

"       "       "       second    53 

— ridges  of  lower  first 54,  55,  56 

"       "       "       second    62 

"       "  upper  first    43,  44 

"       "       second    51 

— lower  first   54 

"       second    62 

- — upper  first    42 

"       second    Si 

Characteristics  common  to  all  of  the  teeth 3 

Cingulum   18 

Color  of  the  deciduous  teeth 133 

Contact,   proximate    19S 

Crown  surfaces 3 

Crowns   of  the  teeth 3 

"             "        lower   incisors    6 

"             "        deciduous  teeth   130 

Cutting  edge  of  the  incisors 6 

Curvature  of  the  gingival  line   3 

Cusp  defined  8 

Cuspid,  lower   38 

"             "     — ridges    39 

"             "     — similarity  to  the  upper 38 

"            "     — surfaces    ^,8,  39 

"             "     — root   40 

upper 33 

"            '■     — distal  surface   36 

"             "     — labial  surface  33 

"            "             "       ridge     33 

"            "    — lingual   surface    34 

"            "    — mesial  surface  35 

"            "    — ridges    34 


INDEX. 


163 


upper 


Cuspid,  upper — root 37 

Deciduous  first  molars  a  distinct  class 129 

"           second  molars   129 

teeth    128 

"             "     — by  what  teeth  succeeded    129 

"              "     — buccal  surfaces     ^32 

"              "     — color    "^^2 

"              "     — lingual  surfaces  132 

"             "    — crowns    ^30 

"             •'    — necks 131 

"             "    — number    ^^^ 

"             "    — roots    ^51 

"       molars — lower  first  buccal   surface    148 

"              "             "         "       bucco-gingival  ridge   148 

"              "             "         "       cusps    148 

"              "             "         "      distal    surface I49 

"             "            "        "      fossae    141 

"■              "             ''         "       grooves     142 

"             "            "        ''      lingual    surface    I49 

"             '■'            "        "      lobes    142 

"              "             "         "       mesial   fossa   I47 

"             "            "        "          "         surface    i49 

"             "            "        ''      occlusal    surface    141 

"              "             "         "       principal  fossa   146 

"              "             "         "       ridges    I43 

buccal   surface    138 

bucco-gingival  ridge   138 

"       cusps  136 

"             "            "        "       distal  surface   140 

"             "            "        "       grooves    I35 

"             "            "        "      lobes    13s 

"              "             "         "       lingual  surface   140 

"             "            "        "      mesial  surface    140 

"             "            "        "       occlusal    surface    I34 

"              "             "         "       ridges    13" 

Dental  arch   •• 187 

"       formulae    ^ 

Developmental  grooves  defined n 

"                      "       of  the  incisors  and  cuspids 21 

"                      "          "         molars     98 

"             lines  defined    11 

"                  "      of  the  incisors  and  cuspids 21 

"                  "          "         first  upper  molar 98 

Dissections    ^58 


164  INDEX. 

Dissections — instruments  necessary  for  158 

"         of  the  bicuspids 166 

"             "        incisors    159 

"            "       lower  molars    179 

"             "        upper    molars 171 

Fissure  defined 1 1 

Fissures,  how  formed  21 

Foramen,  apical    I53 

Formulas,  dental    i 

Fossa  defined 10 

Frenum  labium    208 

lingua:    209 

Gingivse    21  r 

"       — inter-proximate  spaces   212 

Gingival  groove  and  fissure  of  the  upper  lateral  incisor 26 

"        line,  curvature  of  the   3 

"          "      defined    3 

"          "      of  the  upper  central  incisor 20 

Groove  defined  11 

''              "       developmental    11 

"              "      sulcate    II 

"'              "      supplemental    12 

Gums 207 

"     labial  and  buccal   208 

"     lingual  of  lower  jaw  209 

"        "          "  upper  jaw  210 

"     of  what  composed  207 

Incisors,  lower 29 

"            "    — developmental  lines    30 

"            "    — difiference  between  central  and  lateral 29 

"             "     — distal    surface    30 

"             "    — form  of  crown 29 

"            "    — labial  surface  29 

"            ■'    — lingual   surface    30 

"             "     — linguo-gingival  ridge   30 

*'            "    — mesial  surface   30 

"            "    — roots  31 

"         upper  central   16 

"            "            "      — distal  surface  19 

"            "            "      — developmental  lines  or  grooves 21 

"            "            "      — fissures   21 

"            "            "      — form  of  crown   16 

"            "            "      — gingival  line 20 

"            "            "      — labial  surface   17 


INDEX.  165 


Incisors,  upper  central — lingual  fossa   lo 

pit     21 

"            "            "                "       surface    18 

"             "             "      — linguo-gingival  fissure   21 

"             "             "              "               "          ridge    18 

"            "            "      — lobes  of  crown  21 

"             "             "      — marginal  ridges   i<^ 

'•            "            "      — mesial    surface    i9 

"            "                   — root    ^- 

lateral   ^3 

"             "             "      — distal  surface   25 

"             "             "      — division  of  lingual  lobe   26 

"            "            "      — failure  of  lingual  lobe 26 

"            "            "      — general  form  of  crown  ^3 

"             "       — how  different  from  the  central 23 

"            "            "      — labial   surface    24 

"             "             "      — lingual   pit    26 

"            "            "                "        surface   26 

"             "             "      — linguo-gingival  fissure   26 

"            "            "      — mesial    surface    25 

"             '■■             "       — marginal   ridges    26 

"             "             "       — root     ^7 

Inclination  defined  ^9i 

"          mesial — of  the  lower  teeth  192 

"                "            "        upper  teeth     ^91 

Inter-proximate  embrasures  defined  i3> 

"  spaces    

"                      "       defined    ^3 

"                      "      — relation  to  the  forms  of  the  teeth...  i94 

Introduction     •  • ^ 

Lines — developmental    ^  ^ 

"                    "              — of  the  incisors 21 

Lobes  defined -^ 

"       of  the  incisors   ^  ^ 

Lingual  pit  of  the  lateral  incisor 26 

.Linguo-gingival  ridge  of  the  incisors 18,  21 

"            "            "          "       cuspids     34 

"            "        groove    -^^ 

Long-cusped  teeth ^4 

Lobes  of  the  incisors   21 

Man's  diet  ^ 

Marginal  ridges    9 

Mesial  surface  defined 5 

Measurements  of  the  teeth  ^5 

"                "            "    — tables  of   IS 


194 
193 


1 66 


INDEX. 


Mesial 

Molar,   lower   first 


inclination  of  the  lower  teeth 191,  192 

"         upper      "     191,  192 

96 

104 

104 

104 


—buccal  pit   

groove    

"        surface     

— central   fossa    

— cusps   100,   lOI, 

— developmental  grooves   

— distal   surface    

— fissures    

— grooves    

— lingual   surface    

— mesial  surface  

supplemental  fosscC   


— pits    

— triangular  ridges 
— root     


nd 


— buccal  surface   

— cusps    

— developmental    grooves 

— distal    surface 

— fissures     

— lingual   surface    

— lobes    

— mesial    surface    

— occlusal  surface   

— pits    

— root     

— supplemental  fossae   . . . . 
"  grooves    . 

— transverse  ridges   

— triangular  ridges    

— variations   of  form    .  . .  . 


third 


— buccal  surface   . . 
— distal  surface  .  . . 

— five-lobed    

— four-lobed    

— grooves    

— lingual    surface.  . 
— marginal   ridges 


108 
102 
108 
109 

115 
112 
III 
118 
114 
116 
III 
117 
no 

112 
119 
112 
112 
112 
112 

113 
120 

125 
126 
124 
121 
122 
126 
122 


INDEX.  167 


Molar,  lower  third — mesial  surface 126 

"    —root     127 

"             "          '■■    — supernumerary    cusps    123 

"            "         "    — supplemental   fossae    121 

Molar  triangle,  typical  forms '^73 

Molars 66 

— number  and  names 66 

''      — .upper     67 

Molar,   upper  first 68 

"             "          ■'    ^buccal  surface   78 

'•             '■          "    — calcifications   of  lobes 69 

"—cusps   71,72,73.74 

"            "          "    — distal    surface    81 

"    —fifth  lobe  70 

'•            "         "    — fossse    68 

'•'            "         ■'    — grooves    68 

"             "          "    — lingual  surface    79 

"            "         "    — lobes    68 

"            "         "    — mesial  surface   80 

"            "         '■    — occlusal   surface    68 

'•■            "          "    — oblique   ridge    75 

'•    —ridges   7i,  72,  73 

'■            "  second    86 

"            "          "    — abnormal  forms   87 

"            "         "    — buccal  surface    88 

'■             "          '■    — central    fossa 86 

'.'            "         "    — distal  fossa  86 

"            "         "           "      surface    88 

"            "         "   — form  of  neck 89 

"            "         "    — lingual   surface   88 

'•             "          '■'    — mesio-buccal   ridge    89 

"             "          "    — mesial  surface   88 

'■          "    — occlusal   surface    86 

"             "          "    —roots     90 

''            "'         "    — three-cusped    86 

"            "         '•    — variations  of  the  disto-lingual  lobe 86 

"     third    91 

''             "          "    — buccal    surface    93 

"             '■■          ■'    — distal  surface  93 

"             "          '•    — disto-lingual  cusp    9i 

"             "          '■    — irregular   forms    9i 

"            '■          "    — lingual   surface    93 

"             "          "    — mesial    surface    93 

"             "          "    — multiple  roots   94 


105  INDEX. 

Molar,  upper  third — occlusal  surface   > 91 

"            "         "    — root    94 

"            "         "    — three-cusped    91 

"            "         "    — variations  of  form    91 

Neck  of  a  tooth  defined  3 

Nomenclature  •  • i 

Number  of  teeth  of  man 2 

Occlusal  surface  defined 4 

Occlusal   line 189 

"         — relation  of  the  lower  and  upper  teeth 188 

"         — relative  mesio-distal  position  of  the  teeth 190 

Peridental  membrane   206 

Proximate  contact  195 

"               "       defined    5 

"         surfaces  defined  5 

Pulp  chamber 152 

"      — abnormally  long  horns 185 

"      — conditions  which  cause  diminished  size 155 

"      — diminished  size  of,  in  the  adult 154 

"      — dissections  necessary  to  show 157 

"      — divisions  IS3 

"      — early  formative  stages i54 

"      — forms    153 

"      — in  single-rooted  teeth 156 

"      — lateral  openings 184 

"       of  the  upper  incisors 160 

"          "       lower  incisors  164 

■'          "       upper  cuspids    163 

"          "       lower  cuspids 165 

"          "       upper  first  bicuspid  167 

"          "          "       second  bicuspid    168 

"          "       lower  bicuspids  169 

"          "       upper  molars 172 

"          "       lower  molars 180 

"          "       deciduous  teeth 186 

"      — secondary  formations 183 

"      — shortening  of  the  horns 154 

"      — variations  in  the  form 183 

Ridges  defined   9 

"      — how  named  9 

"       — marginal 9 

"      — transverse    9 

"      ■ — triangular 9 

Roots  of  the  teeth  defined  3 


INDEX.  169 


Roots  of  the  teeth — divisions 3 

Root  canal I53 

"         "■    — distal,  of  the  lower  molars 182 

"          "             "             "       upper  molars  176 

"         "    — lateral  openings 184 

"         "    — lingual,  of  the  upper  molars I74 

"         "■    — mesial,  of  the  upper  molars I75 

"         "     of  the  bicuspids,  lower 170 

"         "        "              "            upper  first  167 

second  168 

"         "        "        cuspids,  lower 165 

"         "        "              "        upper 163 

"          "         "         incisors,  lower  164 

"         "        "              "         upper    161 

"         *'        "        molars,  lower  181 

upper    173 

"         "    — size  of,  in  the  incisors 162 

"         "    — position  of,  in  the  upper  molars  I73 

"         "'    — upper  first  molar I73 

"         "            "       second  molar I77 

"      third    molar 178 

"         "    — variations  of  the,  in  the  upper  molars I77 

Short-cusped  teeth  14 

Spaces,  inter-proximate  I93 

"                "                   defined 13 

Sulcate  groove  defined  ". 11 

Sulcus  defined 10 

Supplemental  grooves  defined 12 

Surfaces,  mesial  and  distal,  defined 5 

"         occlusal,  defined 7 

"         of  the  crown,  named 4 

"         proximate,  defined 5 

Tables  of  measurements  of  the  teeth 15 

Teeth — arrangement    •  • 187 

"     — number    2 

Thick-necked    teeth 14 

Thirds — division  of  crown  into 5 

Tissues  of  the  teeth   2 

Tongue-tied    209 

Transverse  ridges  defined 9 

Triangular  ridges  defined 9 

Tubercle  defined  9 

Wrinkles  defined    12 


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